LeetCode [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

 

Constraints:

• 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(int[] nums, int k) {
        int n = nums.length;
        int sum = 0;
        int ret = 0;
        Map<Integer, Integer> map = new HashMap<>();
        map.put(0, 1);
        for(int i=0; i<n; ++i){
            sum += nums[i];
            if(map.containsKey(sum - k)) ret += map.get(sum - k);
            map.put(sum, map.getOrDefault(sum, 0)+1);
        }
        return ret;
    }
}