0500 - 0599
0560 - Subarray Sum Equals K (Medium)
Problem Link
https://leetcode.com/problems/subarray-sum-equals-k/
Problem Statement
Given an array of integers nums and an integer k, return the total number of continuous subarrays whose sum equals to k.
Example 1:
Input: nums = [1,1,1], k = 2
Output: 2Example 2:
Input: nums = [1,2,3], k = 3
Output: 2Constraints:
1 <= nums.length <= 2 * 10^4-1000 <= nums[i] <= 1000-10^7 <= k <= 10^7
Approach 1: Hash Map
We use hash map to store the cumulative sum up to index . If , then it means the sum between indices and is . Therefore, we store the cumulative sum, search for in the hash map and add the occurrences if it is found to the answer.
class Solution {
public:
int subarraySum(vector<int>& nums, int k) {
unordered_map<int, int> m;
m[0]++;
int sum = 0, ans = 0;
for (int i = 0; i < nums.size(); i++) {
sum += nums[i];
ans += m[sum - k];
m[sum]++;
}
return ans;
}
};class Solution {
public int subarraySum(int[] nums, int k) {
int sum = 0, result = 0;
HashMap<Integer, Integer> preSum = new HashMap<>();
preSum.put(0, 1);
for (int i = 0; i < nums.length; i++) {
sum += nums[i];
if (preSum.containsKey(sum - k)) {
result += preSum.get(sum - k);
}
preSum.put(sum, preSum.getOrDefault(sum, 0) + 1);
}
return result;
}
}