Today I have done leetcode's February LeetCoding Challenge with cpp.

February LeetCoding Challenge 10

Description

Subarray Sum Equals K

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: 2

Example 2:

Input: nums = [1,2,3], k = 3
Output: 2

Constraints:

• 1 <= nums.length <= 2 * 10^4
• -1000 <= nums[i] <= 1000
• -10^7 <= k <= 10^7

Solution

class Solution {
public:
  int findPairs(vector<int>& nums, int k) {
    unordered_map<int, int> cnt;
    for(auto i : nums) {
      cnt[i] += 1;
    }

    int answer = 0;
    for(auto [i, c] : cnt) {
      if(k) answer += cnt.count(i + k);
      else answer += c > 1;
    }
    return answer;
  }
};

// Accepted
// 60/60 cases passed (11 ms)Vubmissions
// Your memory usage beats 68.98 % of cpp submissions (13.1 MB)auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
  int subarraySum(vector<int>& nums, int k) {
    unordered_map<int, int> prefixCount{{0, 1}};
    int sum = 0;
    int answer = 0;
    for(auto n : nums) {
      sum += n;
      if(prefixCount.count(sum - k)) {
        answer += prefixCount[sum - k];
      }
      prefixCount[sum] += 1;
    }
    return answer;
  }
};

// Accepted
// 89/89 cases passed (60 ms)
// Your runtime beats 98.77 % of cpp submissions
// Your memory usage beats 39.62 % of cpp submissions (38.3 MB)