算法练习Day28 （Leetcode/Python-贪心算法）

738. Monotone Increasing Digits

An integer has monotone increasing digits if and only if each pair of adjacent digits x and y satisfy x <= y.

Given an integer n, return the largest number that is less than or equal to n with monotone increasing digits.

Example 1:

Input: n = 10
Output: 9

Example 2:

Input: n = 1234
Output: 1234

Example 3:

Input: n = 332
Output: 299

思路，此题求小于给定的数值N的最大的单调递增序列。对于每个数位，从后向前遍历，但凡发现前一位N[i-1]比后一位N[i]大，能做的就是把后一位N[i]置9，前一位置N[i-1]-1。

class Solution(object):
    def monotoneIncreasingDigits(self, n):
        """
        :type n: int
        :rtype: int
        """
        # convert int to string
        strNum = str(n)
        flag = len(strNum)
        for i in range(len(strNum)-1, 0, -1):
            if strNum[i] < strNum[i-1]:
                flag = i 
                strNum = strNum[:i-1] + str(int(strNum[i-1])-1) + strNum[i:]
        
        #for i in range(flag, len(strNum)):
        print(flag)
        strNum = strNum[:flag] + '9' * len( strNum[flag:]) 

        return int(strNum)