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

January LeetCoding Challenge 3

Description

Number of Ways to Split Array

You are given a 0-indexed integer array nums of length n.

nums contains a valid split at index i if the following are true:

• The sum of the first i + 1 elements is greater than or equal to the sum of the last n - i - 1 elements.
• There is at least one element to the right of i. That is, 0 <= i < n - 1.

Return the number of valid splits in nums.

Example 1:

Input: nums = [10,4,-8,7]
Output: 2
Explanation: 
There are three ways of splitting nums into two non-empty parts:
- Split nums at index 0. Then, the first part is [10], and its sum is 10. The second part is [4,-8,7], and its sum is 3. Since 10 >= 3, i = 0 is a valid split.
- Split nums at index 1. Then, the first part is [10,4], and its sum is 14. The second part is [-8,7], and its sum is -1. Since 14 >= -1, i = 1 is a valid split.
- Split nums at index 2. Then, the first part is [10,4,-8], and its sum is 6. The second part is [7], and its sum is 7. Since 6 < 7, i = 2 is not a valid split.
Thus, the number of valid splits in nums is 2.

Example 2:

Input: nums = [2,3,1,0]
Output: 2
Explanation: 
There are two valid splits in nums:
- Split nums at index 1. Then, the first part is [2,3], and its sum is 5. The second part is [1,0], and its sum is 1. Since 5 >= 1, i = 1 is a valid split. 
- Split nums at index 2. Then, the first part is [2,3,1], and its sum is 6. The second part is [0], and its sum is 0. Since 6 >= 0, i = 2 is a valid split.

Constraints:

• 2 <= nums.length <= 105
• -105 <= nums[i] <= 105

Solution

class Solution {
public:
  int numSplits(string s) {
    vector<int> left(26);
    vector<int> right(26);
    int countL = 0;
    int countR = 0;
    for(auto c : s) {
      if(!right[c - 'a']) countR += 1;
      right[c - 'a'] += 1;
    }
    int answer = 0;
    for(auto c : s) {
      if(!left[c - 'a']) countL += 1;
      left[c - 'a'] += 1;
      right[c - 'a'] -= 1;
      if(!right[c - 'a']) countR -= 1;
      if(countL == countR) answer += 1;
      if(countL > countR) break;
    }
    return answer;
  }
};

// Accepted
// 61/61 cases passed (3 ms)
// Your runtime beats 89.96 % of cpp submissions
// Your memory usage beats 63.2 % of cpp submissions (11.3 MB)