738. Monotone Increasing Digits

Medium

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Given a non-negative integer ​​N​​​, find the largest number that is less than or equal to ​​N​​ with monotone increasing digits.

(Recall that an integer has monotone increasing digits if and only if each pair of adjacent digits ​​x​​​ and ​​y​​​ satisfy ​​x <= y​​.)

 

Example 1:

Input: N = 10
Output: 9

 

Example 2:

Input: N = 1234
Output: 1234

 

Example 3:

Input: N = 332
Output: 299

 

Note: ​​N​​​ is an integer in the range ​​[0, 10^9]​​

class Solution {
public:
    int monotoneIncreasingDigits(int N) {
        vector<int> digits;
        int tmp = N;
        while(tmp){
            digits.push_back(tmp % 10);
            tmp = tmp / 10;
        }
        reverse(digits.begin(),digits.end());
        int Index = 0;
        for(;Index < digits.size() - 1;Index ++){
            if(digits[Index] > digits[Index + 1]){
                break;
            }
        }
        if(Index == digits.size() - 1){
            return N;
        }
        digits[Index]--;
        for(int i = Index + 1;i < digits.size();i ++){
            digits[i] = 9;
        }
        for(int i = Index - 1;i >= 0;i --){
            if(digits[i] > digits[i + 1]){
                digits[i + 1] = 9;
                digits[i]--;
            }
        }
        int Result = 0;
        for(int i = 0;i < digits.size();i ++){
            Result = Result * 10 + digits[i];
        }
        return Result;
    }
};