399.除法求值，并查集

Author: linwt

leetcode_Java/DoneTitle.txt

@@ -117,6 +117,7 @@
 347. 前 K 个高频元素
 392. 判断子序列
 394. 字符串解码
+399. 除法求值
 402. 移掉 K 位数字
 406. 根据身高重建队列
 407. 接雨水 II

leetcode_Java/DoneType.txt

@@ -210,4 +210,5 @@
 
 
 十一、图
-207. 课程表（拓扑排序）
+207. 课程表（拓扑排序）
+399. 除法求值（并查集）

leetcode_Java/Solution0399.java

@@ -0,0 +1,89 @@
+// 399. 除法求值
+
+
+class Solution {
+    public double[] calcEquation(List<List<String>> equations, double[] values, List<List<String>> queries) {
+        int size = equations.size();
+        Map<String, Integer> map = new HashMap<>(2 * size);
+        UnionFind unionFind = new UnionFind(2 * size);
+        int id = 0;
+        double[] res = new double[queries.size()];
+        for (List<String> list : equations) {
+            String val1 = list.get(0);
+            String val2 = list.get(1);
+            if (!map.containsKey(val1)) {
+                map.put(val1, id);
+                id++;
+            }
+            if (!map.containsKey(val2)) {
+                map.put(val2, id);
+                id++;
+            }
+        }
+        for (int i = 0; i < size; i++) {
+            int val1 = map.get(equations.get(i).get(0));
+            int val2 = map.get(equations.get(i).get(1));
+            unionFind.union(val1, val2, values[i]);
+        }
+        for (int i = 0; i < queries.size(); i++) {
+            if (map.containsKey(queries.get(i).get(0)) && map.containsKey(queries.get(i).get(1))) {
+                int val1 = map.get(queries.get(i).get(0));
+                int val2 = map.get(queries.get(i).get(1));
+                res[i] = unionFind.getValue(val1, val2);
+            } else {
+                res[i] = -1.0d;
+            }
+        }
+        return res;
+    }
+}
+
+class UnionFind {
+    int[] parent;
+    double[] weight;  // 表示当前节点到根节点的值
+
+    public UnionFind(int size) {
+        this.parent = new int[size];
+        this.weight = new double[size];
+        for (int i = 0; i < size; i++) {
+            parent[i] = i;
+            weight[i] = 1.0d;
+        }
+    }
+
+    //找到当前节点的根节点，在查询的同时进行路径压缩
+    public int find(int x) {
+        if (x != parent[x]) {
+            int temp = parent[x];
+            parent[x] = find(parent[x]);
+            weight[x] = weight[x] * weight[temp];
+        }
+        return parent[x];
+    }
+
+    //将两个节点进行合并
+    public void union(int x, int y, double value) {
+        int rootX = find(x);
+        int rootY = find(y);
+        if (rootX == rootY) {
+            return;
+        } else {
+            parent[rootX] = rootY;
+            weight[rootX] = value * weight[y] / weight[x];
+        }
+    }
+
+    //判断两个节点是否属于同一个分组
+    public boolean isConnected(int x, int y) {
+        return find(x) == find(y);
+    }
+
+    //返回连个节点的比值
+    public double getValue(int x, int y) {
+        if (!isConnected(x, y)) {
+            return -1.0d;
+        } else {
+            return weight[x] / weight[y];
+        }
+    }
+}