[leetcode]494. Target Sum

Analysis

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You are given a list of non-negative integers, a1, a2, …, an, and a target, S. Now you have 2 symbols + and -. For each integer, you should choose one from + and - as its new symbol.
Find out how many ways to assign symbols to make sum of integers equal to target S.

Implement

class Solution {
public:
    int findTargetSumWays(
 
vector<int>& nums, int S) {
        int sum = accumulate(nums.begin(), nums.end(), 0);
        if(sum < S || ((sum+S)&1))
            return 0;
        return counter(nums, (sum+S)>>1);
    }
    int counter(vector<int>& nums, int target){
        vector<int> dp(
 
target+1, 0);
        dp[0] = 1;
        for(int num:nums){
            for(int i=target; i>=num; i--)
                dp[i] += dp[i-num];
        }
        return dp[target];
    }
};