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Author: linwt

2019校招真题编程题汇总_Java/Main008.java

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+package CampusRecruitment2019;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.Arrays;
+import java.util.Scanner;
+
+
+// 牛牛的背包问题
+public class Main008 {
+    public static void main(String[] args) throws IOException {
+        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
+
+        String[] str1 = bufferedReader.readLine().split(" ");
+        int n = Integer.parseInt(str1[0]);
+        long w = Long.parseLong(str1[1]);
+
+        String[] str2 = bufferedReader.readLine().split(" ");
+        long[] v = new long[n];
+        for (int i = 0; i < n; i++)
+            v[i] = Long.parseLong(str2[i]);
+
+        // 计算零食体积总和，总和小于等于背包容量，则有2^n种
+        long sum = 0;
+        for (long l : v)
+            sum += l;
+        if (sum <= w) {
+            System.out.println((long) Math.pow(2, n));
+            return;
+        }
+        // 否则，递归累加计算
+        System.out.println(loop(v, n - 1, w));
+    }
+
+    private static int loop(long[] v, int i, long w) {
+        // 边界条件，最后一袋零食
+        if (i == 0) {
+            // 背包容量≥零食体积，可选择放入或不放入两种情况
+            if (w >= v[0])
+                return 2;
+            // 只能选择不放入一种情况
+            else
+                return 1;
+        }
+        // 边界条件，背包容量为0，只能选择不放入一种情况
+        if (w == 0)
+            return 1;
+
+        // 背包容量足够装下这袋零食，则可选择放入或不放入
+        if (w - v[i] >= 0)
+            return loop(v, i - 1, w - v[i]) + loop(v, i - 1, w);
+        // 否则，只能选择不放入
+        else
+            return loop(v, i - 1, w);
+    }
+}
+
+
+
+/*
+// 动态规划，二维数组
+public class Main008 {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        int n = sc.nextInt(), w = sc.nextInt();
+        int[] v = new int[n];
+        for (int i = 0; i < n; i++) {
+            v[i] = sc.nextInt();
+        }
+
+        int[][] dp = new int[n + 1][w + 1];
+        for (int i = 0; i < n + 1; i++) {
+            dp[i][0] = 1;
+        }
+        for (int j = 0; j <= w; j++) {
+            dp[0][j] = 1;
+        }
+        for (int i = 1; i <= n; i++) {
+            for (int j = 1; j <= w; j++) {
+                dp[i][j] = dp[i - 1][j];
+                if (j - v[i - 1] >= 0) {
+                    dp[i][j] += dp[i - 1][j - v[i - 1]];
+                }
+            }
+        }
+        System.out.println(dp[n][w]);
+    }
+}
+*/
+
+
+
+/*
+// 动态规划，一维数组
+public class Main008 {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        int n = sc.nextInt();
+        int w = sc.nextInt();
+        int[] v = new int[n];
+        for (int i = 0; i < n; i++) {
+            v[i] = sc.nextInt();
+        }
+
+        int[] dp = new int[w + 1];
+        Arrays.fill(dp, 1);
+        for (int i = 0; i < n; i++) {
+            for (int j = w; j >= v[i]; j--) {
+                dp[j] = dp[j] + dp[j - v[i]];
+            }
+        }
+        System.out.println(dp[w]);
+    }
+}
+*/