LeetCode 494. 目标和

//设正整数值为x，那么负整数绝对值为sum - x
//target = x - (sum - x)
//x = (target + sum) / 2
const int N = 1010;
class Solution {
public:
    int dp[N];
    int findTargetSumWays(vector<int>& nums, int target) {
        int sum = 0;
        for (int i = 0; i < nums.size(); i ++) sum += nums[i];

        if ((sum + target) % 2 != 0) return 0;
        if (abs(target) > sum) return 0;

        int size = (target + sum) / 2;
        if (size < 0) return 0; //size只能为正整数
        
        dp[0] = 1; //target为0有一种情况

        for (int i = 0; i < nums.size(); i ++)
            for (int j = size; j >= nums[i]; j --)
                dp[j] += dp[j - nums[i]];


        return dp[size];
    }
};