LeetCode 560. Subarray Sum Equals K

最新推荐文章于 2025-04-22 09:11:01 发布

WX_ming

最新推荐文章于 2025-04-22 09:11:01 发布

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本文介绍了一种高效算法来解决子数组和等于特定值K的问题。通过使用哈希表记录连续子数组的和，可以快速查找满足条件的子数组数量。文章详细解释了算法流程，并提供了完整的C++代码实现。

#560. Subarray Sum Equals K
Given an array of integers and an integer k, you need to find the total number of continuous subarrays whose sum equals to k.

Example 1:
Input:nums = [1,1,1], k = 2
Output: 2
Note:
The length of the array is in range [1, 20,000].
The range of numbers in the array is [-1000, 1000] and the range of the integer k is [-1e7, 1e7].

Approach

题目大意：给你一组数据，然后问你连续子串和为K的数量
思路方法：用一个sum装连续和，我们需要一个hashmap记录相同sum的次数，然后每次查找sum-k的次数并相加，最后就是答案

Code

class Solution {
public:
	int subarraySum(vector<int>& nums, int k) {
		unordered_map<int, int>unmp;
		int sum = 0;
		int cnt = 0;
		unmp[0] = 1;
		for (int i = 0; i < nums.size(); i++) {
			sum += nums[i];
			int target = sum - k;
			if (unmp.find(target) != unmp.end()) {
				cnt += unmp[target];
			}
			unmp[sum]++;
		}
		return cnt;
	}
};