【C++ STL 模板类】pair 键值对

题目：

题解：

func findTargetSumWays(nums []int, target int) int {
    sum := 0
    for _, v := range nums {
        sum += v
    }
    diff := sum - target
    if diff < 0 || diff%2 == 1 {
        return 0
    }
    neg := diff / 2
    dp := make([]int, neg+1)
    dp[0] = 1
    for _, num := range nums {
        for j := neg; j >= num; j-- {
            dp[j] += dp[j-num]
        }
    }
    return dp[neg]
}