No.149 - LeetCode560

func subarraySum(nums []int, k int) int {
    mp := make(map[int]int)
    ans := 0
    sum := 0
    mp[0] = 1
    for i:=0;i<len(nums);i++{
        sum += nums[i]
        ans += mp[sum - k]
        mp[sum] ++
    }
    return ans
}