Google算法题：目标和

来源：互联网发布：php走势图源码编辑：程序博客网时间：2024/06/06 00:15

题目

题目来源：Link

分析

代码

package com.graph;import java.util.*;public class Solution{int sum=0;int count=0;int tar;int[] as;int n;//方法一：树的遍历，剪枝//递归public void solve(int[] as, int tar){this.tar = tar;this.as = as;if(as==null || as.length==0)System.out.println(count);n = as.length;handle(0);System.out.println(count);}public void handle(int i){if(i==n){if(sum==tar)count++;return;}//减枝//当剩余数的最大和最小无法满足要求时，返回int tmpSum = getSum(i);if(sum-tmpSum>tar || sum+tmpSum<tar){return;}//将i设为+号，其实就是preOrder遍历//遍历+号边sum = sum+as[i];handle(i+1);sum = sum-as[i];//遍历-号边sum = sum-as[i];handle(i+1);sum = sum+as[i];}//可优化，变成一个数组存着，然后取用public int getSum(int k){int tmpSum = 0;for(int i=k; i<n; i++){tmpSum+=as[i];}return tmpSum;}//方法二：动态规划public void solve_dp(int[] as, int tar){this.tar = tar;this.as = as;if(as==null || as.length==0)return;n = as.length;int tmpSum = getSum(n);if(tmpSum<Math.abs(tar))return;int dSum = tmpSum<<1;int[][] dp = new int[n][dSum+1];if(as[0]==0) {dp[0][tmpSum] = 2;}else {dp[0][sum-as[0]] = 1;dp[0][sum+as[0]] = 1;}for(int i=0; i<n; i++) {for(int j=0; j<dSum+1; j++) {if(j-as[i]>=0) {dp[i][j]+=dp[i-1][j-as[i]];}if(j+as[i]<=dSum) {dp[i][j]+=dp[i-1][j+as[i]];}}}count = dp[n-1][tar+sum];System.out.println(count);}public static void main(String[] args) {Solution s = new Solution();s.solve(new int[] {1,1,1,1,1}, 3);}}

阅读全文

0 0