560. Subarray Sum Equals K

560. Subarray Sum Equals K (Medium)

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].

Companies:
Facebook, Bloomberg, Amazon, Twilio, Apple, Microsoft, Yandex, Expedia

Related Topics:
Array, Hash Table

Similar Questions:

• Two Sum (Easy)
• Continuous Subarray Sum (Medium)
• Subarray Product Less Than K (Medium)
• Find Pivot Index (Easy)
• Subarray Sums Divisible by K (Medium)

Solution 1.

// OJ: https://leetcode.com/problems/subarray-sum-equals-k/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(N)
class Solution {
public:
    int subarraySum(vector<int>& nums, int k) {
        int ans = 0, sum = 0;
        unordered_map<int, int> m{{0, 1}};
        for (int n : nums) {
            sum += n;
            auto it = m.find(sum - k);
            if (it != m.end()) ans += it->second;
            m[sum]++;
        }
        return ans;
    }
};