LeetCode-in-Kotlin · javadev · May 31, 2023 · May 31, 2023
diff --git a/README.md b/README.md
diff --git a/src/main/kotlin/g0001_0100/s0001_two_sum/readme.md b/src/main/kotlin/g0001_0100/s0001_two_sum/readme.md
@@ -49,7 +49,7 @@ class Solution {
         for (i in numbers.indices) {
             val requiredNum = target - numbers[i]
             if (indexMap.containsKey(requiredNum)) {
-                return intArrayOf(indexMap[requiredNum]!!, i)
+                return intArrayOf(indexMap.getValue(requiredNum), i)
             }
             indexMap[numbers[i]] = i
         }

diff --git a/src/main/kotlin/g0001_0100/s0014_longest_common_prefix/readme.md b/src/main/kotlin/g0001_0100/s0014_longest_common_prefix/readme.md
@@ -43,7 +43,7 @@ class Solution {
         var temp = strs[0]
         var i = 1
         var cur: String
-        while (temp.length > 0 && i < strs.size) {
+        while (temp.isNotEmpty() && i < strs.size) {
             if (temp.length > strs[i].length) {
                 temp = temp.substring(0, strs[i].length)
             }

diff --git a/src/main/kotlin/g0001_0100/s0020_valid_parentheses/readme.md b/src/main/kotlin/g0001_0100/s0020_valid_parentheses/readme.md
@@ -59,11 +59,11 @@ class Solution {
             val c = element
             if (c == '(' || c == '[' || c == '{') {
                 stack.push(c)
-            } else if (c == ')' && !stack.isEmpty() && stack.peek() == '(') {
+            } else if (c == ')' && stack.isNotEmpty() && stack.peek() == '(') {
                 stack.pop()
-            } else if (c == '}' && !stack.isEmpty() && stack.peek() == '{') {
+            } else if (c == '}' && stack.isNotEmpty() && stack.peek() == '{') {
                 stack.pop()
-            } else if (c == ']' && !stack.isEmpty() && stack.peek() == '[') {
+            } else if (c == ']' && stack.isNotEmpty() && stack.peek() == '[') {
                 stack.pop()
             } else {
                 return false

diff --git a/src/main/kotlin/g0001_0100/s0049_group_anagrams/readme.md b/src/main/kotlin/g0001_0100/s0049_group_anagrams/readme.md
@@ -46,7 +46,7 @@ class Solution {
             hm.computeIfAbsent(
                 temp
             ) { _: String? -> ArrayList() }
-            hm[temp]!!.add(s)
+            hm.getValue(temp).add(s)
         }
         return ArrayList<List<String>>(hm.values)
     }

diff --git a/src/main/kotlin/g0001_0100/s0071_simplify_path/readme.md b/src/main/kotlin/g0001_0100/s0071_simplify_path/readme.md
@@ -68,7 +68,7 @@ class Solution {
             }
             val s = path.substring(start, end)
             if (s == "..") {
-                if (!stk.isEmpty()) {
+                if (stk.isNotEmpty()) {
                     stk.pop()
                 }
             } else if (s != "." && s != "") {
@@ -77,7 +77,7 @@ class Solution {
             start = end + 1
         }
         val ans = StringBuilder()
-        while (!stk.isEmpty()) {
+        while (stk.isNotEmpty()) {
             ans.insert(0, stk.pop())
             ans.insert(0, "/")
         }

diff --git a/src/main/kotlin/g0101_0200/s0102_binary_tree_level_order_traversal/readme.md b/src/main/kotlin/g0101_0200/s0102_binary_tree_level_order_traversal/readme.md
@@ -61,9 +61,9 @@ class Solution {
         queue.add(localRoot)
         queue.add(null)
         var level: MutableList<Int> = ArrayList()
-        while (!queue.isEmpty()) {
+        while (queue.isNotEmpty()) {
             localRoot = queue.remove()
-            while (!queue.isEmpty() && localRoot != null) {
+            while (queue.isNotEmpty() && localRoot != null) {
                 level.add(localRoot.`val`)
                 if (localRoot.left != null) {
                     queue.add(localRoot.left)
@@ -75,7 +75,7 @@ class Solution {
             }
             result.add(level)
             level = ArrayList()
-            if (!queue.isEmpty()) {
+            if (queue.isNotEmpty()) {
                 queue.add(null)
             }
         }

diff --git a/...main/kotlin/g0101_0200/s0103_binary_tree_zigzag_level_order_traversal/readme.md b/...main/kotlin/g0101_0200/s0103_binary_tree_zigzag_level_order_traversal/readme.md
@@ -60,9 +60,9 @@ class Solution {
         q.add(null)
         var zig = true
         var level = LinkedList<Int>()
-        while (!q.isEmpty()) {
+        while (q.isNotEmpty()) {
             var node: TreeNode? = q.remove()
-            while (!q.isEmpty() && node != null) {
+            while (q.isNotEmpty() && node != null) {
                 if (zig) {
                     level.add(node.`val`)
                 } else {
@@ -79,7 +79,7 @@ class Solution {
             result.add(level)
             zig = !zig
             level = LinkedList()
-            if (!q.isEmpty()) {
+            if (q.isNotEmpty()) {
                 q.add(null)
             }
         }

diff --git a/..._0200/s0105_construct_binary_tree_from_preorder_and_inorder_traversal/readme.md b/..._0200/s0105_construct_binary_tree_from_preorder_and_inorder_traversal/readme.md
@@ -50,8 +50,9 @@ import java.util.HashMap
 class Solution {
     private var j = 0
     private val map: MutableMap<Int, Int> = HashMap()
+
     fun get(key: Int): Int {
-        return map[key]!!
+        return map.getValue(key)
     }
 
     private fun answer(preorder: IntArray, inorder: IntArray, start: Int, end: Int): TreeNode? {

diff --git a/src/main/kotlin/g0101_0200/s0111_minimum_depth_of_binary_tree/readme.md b/src/main/kotlin/g0101_0200/s0111_minimum_depth_of_binary_tree/readme.md
@@ -55,7 +55,7 @@ class Solution {
         val queue: Queue<TreeNode> = LinkedList()
         queue.add(root)
         var d = 0
-        while (!queue.isEmpty()) {
+        while (queue.isNotEmpty()) {
             val size: Int = queue.size
             for (i in 0 until size) {
                 val current: TreeNode = queue.poll()

diff --git a/...otlin/g0101_0200/s0117_populating_next_right_pointers_in_each_node_ii/readme.md b/...otlin/g0101_0200/s0117_populating_next_right_pointers_in_each_node_ii/readme.md
@@ -62,7 +62,7 @@ class Solution {
         root.next = null
         var temp: Node?
         var prev: Node?
-        while (!bfsQueue.isEmpty()) {
+        while (bfsQueue.isNotEmpty()) {
             val size = bfsQueue.size
             prev = null
             for (j in 0 until size) {

diff --git a/src/main/kotlin/g0101_0200/s0126_word_ladder_ii/readme.md b/src/main/kotlin/g0101_0200/s0126_word_ladder_ii/readme.md
@@ -69,7 +69,7 @@ class Solution {
         // find endWord flag
         var findEnd = false
         // traverse current layer nodes
-        while (!queue.isEmpty()) {
+        while (queue.isNotEmpty()) {
             val word = queue.remove()
             for (next in wordSet) {
                 // is ladder words

diff --git a/src/main/kotlin/g0101_0200/s0127_word_ladder/readme.md b/src/main/kotlin/g0101_0200/s0127_word_ladder/readme.md
@@ -55,7 +55,7 @@ class Solution {
         val strLen = beginWord.length
         beginSet.add(beginWord)
         endSet.add(endWord)
-        while (!beginSet.isEmpty() && !endSet.isEmpty()) {
+        while (beginSet.isNotEmpty() && endSet.isNotEmpty()) {
             if (beginSet.size > endSet.size) {
                 val temp = beginSet
                 beginSet = endSet

diff --git a/src/main/kotlin/g0101_0200/s0128_longest_consecutive_sequence/readme.md b/src/main/kotlin/g0101_0200/s0128_longest_consecutive_sequence/readme.md
@@ -45,7 +45,7 @@ class Solution {
         var lastNum = Integer.MIN_VALUE
         var length = 0
         var maxLength = 1
-        while (!queue.isEmpty()) {
+        while (queue.isNotEmpty()) {
             val num = queue.poll()
             if (num == lastNum) {
                 continue

diff --git a/src/main/kotlin/g0101_0200/s0144_binary_tree_preorder_traversal/readme.md b/src/main/kotlin/g0101_0200/s0144_binary_tree_preorder_traversal/readme.md
@@ -58,7 +58,7 @@ class Solution {
         }
         val stack: Stack<TreeNode> = Stack<TreeNode>()
         var current: TreeNode? = root
-        while (current != null || !stack.isEmpty()) {
+        while (current != null || stack.isNotEmpty()) {
             while (current != null) {
                 result.add(current.`val`)
                 stack.push(current.right)

diff --git a/src/main/kotlin/g0101_0200/s0150_evaluate_reverse_polish_notation/readme.md b/src/main/kotlin/g0101_0200/s0150_evaluate_reverse_polish_notation/readme.md
@@ -72,7 +72,7 @@ class Solution {
             if (op.contains(t)) {
                 val b = stack.removeFirst().toInt()
                 val a = stack.removeFirst().toInt()
-                val c = op[t]!!.apply(a, b)
+                val c = op.getValue(t).apply(a, b)
                 stack.addFirst(c.toString())
             } else {
                 stack.addFirst(t)

diff --git a/src/main/kotlin/g0101_0200/s0166_fraction_to_recurring_decimal/readme.md b/src/main/kotlin/g0101_0200/s0166_fraction_to_recurring_decimal/readme.md
@@ -63,7 +63,7 @@ class Solution {
         val map: MutableMap<Long, Int> = HashMap()
         while (remainder != 0L) {
             if (map.containsKey(remainder)) {
-                sb.insert(map[remainder]!!, "(")
+                sb.insert(map.getValue(remainder), "(")
                 sb.append(")")
                 break
             }

diff --git a/src/main/kotlin/g0201_0300/s0216_combination_sum_iii/readme.md b/src/main/kotlin/g0201_0300/s0216_combination_sum_iii/readme.md
@@ -67,7 +67,7 @@ class Solution {
             return
         }
         if (n == 0 && tmp.size == k) {
-            a.add(tmp.map { it -> it }.toMutableList())
+            a.add(tmp.map { it }.toMutableList())
             return
         }
         for (i in index until 10) {

diff --git a/src/main/kotlin/g0201_0300/s0220_contains_duplicate_iii/readme.md b/src/main/kotlin/g0201_0300/s0220_contains_duplicate_iii/readme.md
@@ -67,10 +67,10 @@ class Solution {
             if (d.containsKey(m)) {
                 return true
             }
-            if (d.containsKey(m - 1) && Math.abs(nums[i] - d[m - 1]!!) < w) {
+            if (d.containsKey(m - 1) && Math.abs(nums[i] - d.getValue(m - 1)) < w) {
                 return true
             }
-            if (d.containsKey(m + 1) && Math.abs(nums[i] - d[m + 1]!!) < w) {
+            if (d.containsKey(m + 1) && Math.abs(nums[i] - d.getValue(m + 1)) < w) {
                 return true
             }
             d[m] = nums[i].toLong()

diff --git a/src/main/kotlin/g0201_0300/s0239_sliding_window_maximum/readme.md b/src/main/kotlin/g0201_0300/s0239_sliding_window_maximum/readme.md
@@ -59,7 +59,7 @@ class Solution {
         var i = 0
         var j = 0
         while (j < nums.size) {
-            while (!dq.isEmpty() && dq.peekLast() < nums[j]) {
+            while (dq.isNotEmpty() && dq.peekLast() < nums[j]) {
                 dq.pollLast()
             }
             dq.addLast(nums[j])

diff --git a/src/main/kotlin/g0201_0300/s0241_different_ways_to_add_parentheses/readme.md b/src/main/kotlin/g0201_0300/s0241_different_ways_to_add_parentheses/readme.md
@@ -45,7 +45,7 @@ class Solution {
 
     private fun diffWayToCompute(expression: String, hashMap: HashMap<String, List<Int>>): List<Int> {
         if (hashMap.containsKey(expression)) {
-            return hashMap[expression]!!
+            return hashMap.getValue(expression)
         }
         val newList = arrayListOf<Int>()
         if (!hasOperatorInBetween(expression)) {

diff --git a/src/main/kotlin/g0201_0300/s0282_expression_add_operators/readme.md b/src/main/kotlin/g0201_0300/s0282_expression_add_operators/readme.md
@@ -46,7 +46,7 @@ Note that operands in the returned expressions **should not** contain leading ze
 class Solution {
     fun addOperators(num: String, target: Int): List<String> {
         val res: MutableList<String> = ArrayList()
-        if (num.length == 0 || java.lang.Long.valueOf(num) > Int.MAX_VALUE) {
+        if (num.isEmpty() || java.lang.Long.valueOf(num) > Int.MAX_VALUE) {
             return res
         }
         val list = num.toCharArray()

diff --git a/src/main/kotlin/g0301_0400/s0332_reconstruct_itinerary/readme.md b/src/main/kotlin/g0301_0400/s0332_reconstruct_itinerary/readme.md
@@ -69,7 +69,7 @@ class Solution {
 
     private fun dfs(map: Map<String, PriorityQueue<String>>, src: String, ans: LinkedList<String>) {
         val temp = map[src]
-        while (temp != null && !temp.isEmpty()) {
+        while (!temp.isNullOrEmpty()) {
             val nbr = temp.remove()
             dfs(map, nbr, ans)
         }

diff --git a/src/main/kotlin/g0301_0400/s0350_intersection_of_two_arrays_ii/readme.md b/src/main/kotlin/g0301_0400/s0350_intersection_of_two_arrays_ii/readme.md
@@ -45,7 +45,7 @@ class Solution {
         for (i in 0 until nums2.size) {
             if (a.getOrDefault(nums2[i], 0)> 0) {
                 s.add(nums2[i])
-                a[nums2[i]] = a[nums2[i]]!! - 1
+                a[nums2[i]] = a.getValue(nums2[i]) - 1
             }
         }
         return s.toIntArray()

diff --git a/src/main/kotlin/g0301_0400/s0355_design_twitter/readme.md b/src/main/kotlin/g0301_0400/s0355_design_twitter/readme.md
@@ -75,7 +75,7 @@ class Twitter {
     fun getNewsFeed(userId: Int): List<Int> {
         checkNewUser(userId)
         val res: MutableList<Int> = ArrayList()
-        val followers = twitterData[userId]!!
+        val followers = twitterData.getValue(userId)
         var t = head.next
         while (t != null && res.size < 10) {
             if (followers.contains(t.userId)) {
@@ -89,7 +89,7 @@ class Twitter {
     fun follow(followerId: Int, followeeId: Int) {
         checkNewUser(followeeId)
         checkNewUser(followerId)
-        twitterData[followerId]!!.add(followeeId)
+        twitterData.getValue(followerId).add(followeeId)
     }
 
     fun unfollow(followerId: Int, followeeId: Int) {
@@ -99,7 +99,7 @@ class Twitter {
             return
         }
         checkNewUser(followerId)
-        twitterData[followerId]!!.remove(followeeId)
+        twitterData.getValue(followerId).remove(followeeId)
     }
 
     fun checkNewUser(userId: Int) {
@@ -108,7 +108,7 @@ class Twitter {
         }
         twitterData[userId] = HashSet()
         // follow  yourself
-        twitterData[userId]!!.add(userId)
+        twitterData.getValue(userId).add(userId)
     }
 }
 

diff --git a/src/main/kotlin/g0301_0400/s0373_find_k_pairs_with_smallest_sums/readme.md b/src/main/kotlin/g0301_0400/s0373_find_k_pairs_with_smallest_sums/readme.md
@@ -74,7 +74,7 @@ class Solution {
             }
         }
         var i = 1
-        while (i <= k && !queue.isEmpty()) {
+        while (i <= k && queue.isNotEmpty()) {
             val cur = queue.poll()
             res.add(cur.al)
             val next = cur.index

diff --git a/src/main/kotlin/g0301_0400/s0388_longest_absolute_file_path/readme.md b/src/main/kotlin/g0301_0400/s0388_longest_absolute_file_path/readme.md
@@ -117,17 +117,17 @@ class Solution {
             if (nextLevel < currLevel) {
                 var j = 0
                 if (isFile) {
-                    while (!stack.isEmpty() && j < currLevel - nextLevel) {
+                    while (stack.isNotEmpty() && j < currLevel - nextLevel) {
                         currDirLen -= stack.pop()
                         j++
                     }
                 } else {
-                    while (!stack.isEmpty() && j <= currLevel - nextLevel) {
+                    while (stack.isNotEmpty() && j <= currLevel - nextLevel) {
                         currDirLen -= stack.pop()
                         j++
                     }
                 }
-            } else if (nextLevel == currLevel && !isFile && !stack.isEmpty()) {
+            } else if (nextLevel == currLevel && !isFile && stack.isNotEmpty()) {
                 currDirLen -= stack.pop()
             }
             if (nextLevel == 0) {

diff --git a/src/main/kotlin/g0401_0500/s0407_trapping_rain_water_ii/readme.md b/src/main/kotlin/g0401_0500/s0407_trapping_rain_water_ii/readme.md
@@ -69,7 +69,7 @@ class Solution {
             visited1[r][cols - 1] = true
         }
         // end build wall
-        while (!walls.isEmpty()) {
+        while (walls.isNotEmpty()) {
             val min = walls.poll()
             visit(heightMap, min, walls)
         }

diff --git a/src/main/kotlin/g0401_0500/s0429_n_ary_tree_level_order_traversal/readme.md b/src/main/kotlin/g0401_0500/s0429_n_ary_tree_level_order_traversal/readme.md
@@ -51,7 +51,7 @@ class Solution {
         }
         val queue: Queue<Node> = LinkedList<Node>()
         queue.offer(root)
-        while (!queue.isEmpty()) {
+        while (queue.isNotEmpty()) {
             val size: Int = queue.size
             val level: MutableList<Int> = ArrayList()
             for (i in 0 until size) {

diff --git a/src/main/kotlin/g0401_0500/s0433_minimum_genetic_mutation/readme.md b/src/main/kotlin/g0401_0500/s0433_minimum_genetic_mutation/readme.md
@@ -69,7 +69,7 @@ class Solution {
         val queue: Queue<String> = LinkedList()
         queue.offer(start)
         var step = 0
-        while (!queue.isEmpty()) {
+        while (queue.isNotEmpty()) {
             var curSize = queue.size
             while (curSize-- > 0) {
                 val cur = queue.poll()

diff --git a/src/main/kotlin/g0401_0500/s0434_number_of_segments_in_a_string/readme.md b/src/main/kotlin/g0401_0500/s0434_number_of_segments_in_a_string/readme.md
@@ -37,13 +37,13 @@ class Solution {
     fun countSegments(s: String): Int {
         var s = s
         s = s.trim { it <= ' ' }
-        if (s.length == 0) {
+        if (s.isEmpty()) {
             return 0
         }
         val splitted = s.split(" ".toRegex()).dropLastWhile { it.isEmpty() }.toTypedArray()
         var result = 0
         for (value in splitted) {
-            if (value.length > 0) {
+            if (value.isNotEmpty()) {
                 result++
             }
         }

diff --git a/src/main/kotlin/g0401_0500/s0456_132_pattern/readme.md b/src/main/kotlin/g0401_0500/s0456_132_pattern/readme.md
@@ -59,7 +59,7 @@ class Solution {
             if (nums[i] < s3) {
                 return true
             } else {
-                while (!stack.isEmpty() && nums[i] > stack.peek()) {
+                while (stack.isNotEmpty() && nums[i] > stack.peek()) {
                     s3 = Math.max(s3, stack.pop())
                 }
             }

diff --git a/src/main/kotlin/g0401_0500/s0468_validate_ip_address/readme.md b/src/main/kotlin/g0401_0500/s0468_validate_ip_address/readme.md
@@ -50,7 +50,7 @@ For example, "`2001:0db8:85a3:0000:0000:8a2e:0370:7334"` and "`2001:db8:85a3:0:0
 ```kotlin
 class Solution {
     fun validIPAddress(ip: String): String {
-        if (ip.length == 0) {
+        if (ip.isEmpty()) {
             return NEITHER
         }
         val arr = ip.split("\\.".toRegex()).toTypedArray()

diff --git a/src/main/kotlin/g0401_0500/s0488_zuma_game/readme.md b/src/main/kotlin/g0401_0500/s0488_zuma_game/readme.md
@@ -63,10 +63,10 @@ class Solution {
     }
 
     private fun findMinStepDp(board: String, hand: String, dp: MutableMap<String, MutableMap<String, Int?>?>): Int {
-        if (board.length == 0) {
+        if (board.isEmpty()) {
             return 0
         }
-        if (hand.length == 0) {
+        if (hand.isEmpty()) {
             return -1
         }
         if (dp[board] != null && dp[board]!![hand] != null) {