560. Subarray Sum Equals K

最新推荐文章于 2020-07-21 10:35:30 发布

转载最新推荐文章于 2020-07-21 10:35:30 发布 · 168 阅读

本文介绍了一种高效算法来解决子数组求和等于特定值K的问题。使用哈希表跟踪累积和出现的次数，从而快速找出所有连续子数组中和为K的数量。这种方法不仅避免了传统双重循环的时间复杂度过高问题，而且可以处理大规模数据集。

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].

class Solution {
public:
    int subarraySum(vector<int>& nums, int k) {
        unordered_map<int,int> sumTracker;
        int ret =0;
        int sum =0;
        sumTracker[0] = 1;
        for(auto& num: nums)
        {
            sum += num;
            if(sumTracker[sum - k])
            {
                ret += sumTracker[sum - k] ;
            }
            sumTracker[sum]++;
        }
        
        return ret;
        
    }
};