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].

Acumulative Sum

public int subarraySum3(int[] nums, int k) {
    int result = 0;
    for(int i = 0; i < nums.length; i++) {
        int sum = 0;
        for(int j = i; j < nums.length; j++) {
            sum += nums[j];
            if(sum == k) result++;
        }
    }
    return result;
}

HashMap

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