Leetcode 1323 Mximum 69 Number (由6和9组成的最大数字)（Math)

Leetcode 1323 Mximum 69 Number （Math)

题目描述

Given a positive integer num consisting only of digits 6 and 9.

Return the maximum number you can get by changing at most one digit (6 becomes 9, and 9 becomes 6).

例子

Example 1:

Input: num = 9669
Output: 9969
Explanation: 
Changing the first digit results in 6669.
Changing the second digit results in 9969.
Changing the third digit results in 9699.
Changing the fourth digit results in 9666. 
The maximum number is 9969.

Example 2:
Input: num = 9996
Output: 9999
Explanation: Changing the last digit 6 to 9 results in the maximum number.

Example 3:
Input: num = 9999
Output: 9999
Explanation: It is better not to apply any change.

限制条件

Constraints:
1 <= num <= 10^4
num's digits are 6 or 9.

解题思路

将num中最高位的6变成9

代码

Java 代码
class Solution {
    public int maximum69Number (int num) {
        char[] chr = Integer.toString(num).toCharArray();
        for(int i=0; i<chr.length; ++i){
            if ( chr[i] == '6' ){
                chr[i] = '9';
                break;
            }
        }
        return Integer.parseInt(chr.toString());
    }
}

Python代码
class Solution:
    def maximum69Number (self, num: int) :
        return int(str(num).replace('6', '9', 1))
``