leetcode: 560. Subarray Sum Equals K DescriptionHintsSubmissionsDiscussSolution Given an array of in

560. Subarray Sum Equals K

DescriptionHintsSubmissionsDiscussSolution

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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:

1. The length of the array is in range [1, 20,000].
2. 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) {
        
        int result = 0;
        int curSum = 0;
        map<int, int> preSum;
        
        preSum[0] = 1;
        
        for (int i:nums) {
            curSum += i;
            
            if (preSum.find(curSum-k) != preSum.end()) {
                result += preSum[curSum-k];
            }
            
            if (preSum.find(curSum) == preSum.end()) {
                preSum[curSum] = 1;
            }
            else {
                preSum[curSum]++;
            }
        }
        
        return result;
    }
};