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

June LeetCoding Challenge 16

Description

Maximum Difference Between Increasing Elements

Given a 0-indexed integer array nums of size n, find the maximum difference between nums[i] and nums[j] (i.e., nums[j] - nums[i]), such that 0 <= i < j < n and nums[i] < nums[j].

Return the maximum difference. If no such i and j exists, return -1.

Example 1:

Input: nums = [7,1,5,4]
Output: 4
Explanation:
The maximum difference occurs with i = 1 and j = 2, nums[j] - nums[i] = 5 - 1 = 4.
Note that with i = 1 and j = 0, the difference nums[j] - nums[i] = 7 - 1 = 6, but i > j, so it is not valid.

Example 2:

Input: nums = [9,4,3,2]
Output: -1
Explanation:
There is no i and j such that i < j and nums[i] < nums[j].

Example 3:

Input: nums = [1,5,2,10]
Output: 9
Explanation:
The maximum difference occurs with i = 0 and j = 3, nums[j] - nums[i] = 10 - 1 = 9.

Constraints:

• n == nums.length
• 2 <= n <= 1000
• 1 <= nums[i] <= 109

Solution

class Solution {
public:
  int maxDiff(int num) {
    string n = to_string(num);
    string maxN = n;
    int len = n.length();
    int start = 0;
    while(start < len && maxN[start] == '9') start += 1;
    for(int i = start + 1; i < len; ++i) {
      if(maxN[i] == maxN[start]) maxN[i] = '9';
    }
    if(start < len) maxN[start] = '9';

    string minN = n;
    bool changed = false;
    for(int i = 0; i < len && !changed; ++i) {
      char target = minN[i];
      if(!i) {
        if(target == '1') continue;
        changed = true;
        for(int j = 0; j < len; ++j) {
          if(minN[j] == target) minN[j] = '1';
        }
      } else {
        if(target == '0' || target == minN[0]) continue;
        changed = true;
        for(int j = 0; j < len; ++j) {
          if(minN[j] == target) minN[j] = '0';
        }
      }
    }
    return stoi(maxN) - stoi(minN);
  }
};

// Accepted
// 211/211 cases passed (0 ms)
// Your runtime beats 100 % of cpp submissions
// Your memory usage beats 66.9 % of cpp submissions (8.2 MB)