【代码随想录day 35】 力扣 494. 目标和

视频讲解：https://www.bilibili.com/video/BV1o8411j73x/?vd_source=a935eaede74a204ec74fd041b917810c
文档讲解：https://programmercarl.com/0494.%E7%9B%AE%E6%A0%87%E5%92%8C.html#%E6%80%9D%E8%B7%AF
力扣题目：https://leetcode.cn/problems/target-sum/

class Solution {
public:int findTargetSumWays(vector<int>& nums, int target) {int sum = 0;for(int i = 0; i < nums.size(); ++i){sum += nums[i];}if (abs(target) > sum) return 0; // 此时没有方案if ((target + sum) % 2 == 1) return 0; // 此时没有方案int bagSize = (target + sum) / 2;//1.dp定义：dp[i][j]表示背包容量为j，前i个元素放满有dp[i][j]种方法vector<vector<int>> dp(nums.size(), vector<int>(bagSize + 1, 0));//2.递推公式：dp[i][j] = dp[i - 1][j] + dp[i][j - nums[i]];//3.初始化// 初始化最上行if (nums[0] <= bagSize) {dp[0][nums[0]] = 1; }// 初始化最左列，最左列其他数值在递推公式中就完成了赋值dp[0][0] = 1; int numZero = 0;for (int i = 0; i < nums.size(); i++) {if (nums[i] == 0) numZero++;dp[i][0] = (int) pow(2.0, numZero);}//4.遍历，从上往下for(int i = 1; i < nums.size();  ++i){for(int j = 0; j <=bagSize; ++j){if(j < nums[i]){dp[i][j] = dp[i - 1][j];}else{dp[i][j] = dp[i - 1][j] + dp[i - 1][j - nums[i]];}}}return dp[nums.size() - 1][bagSize];}
};