062_和为K的子数组

知识点：前缀和、哈希表

LeetCode第五百六十题：https://leetcode-cn.com/problems/subarray-sum-equals-k/submissions/

语言：GoLang

// 前缀和 + 哈希表
func subarraySum(nums []int, k int) int {
    length := len(nums)

    hMap, preSum, count := map[int]int{0: 1}, 0, 0
    for i := 1; i <= length; i++ {
        preSum = nums[i - 1] + preSum
        if value, ok := hMap[preSum - k]; ok {
            count += value
        }
        hMap[preSum]++
    }

    return count
}




// 朴素解法，O(n^2)
func subarraySum_0(nums []int, k int) int {
    length := len(nums)

    count := 0
    for i := 0; i < length; i++ {
        sum := 0
        for j := i; j < length; j++ {
            sum += nums[j]
            if sum == k {
                count++
            }
        }
    }

    return count
}