題目
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).
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.
Constraints:
1 <= num <= 10^4
num's digits are 6 or 9.
分析
題意：給一個正整數，只包含9和6，僅改變其中一個數字，使其最大。
很簡單，從高到低判斷是否爲9即可，如果是，則判斷下一位，如果不是，則改成9，並返回。
涉及到字符串和整型的轉換。
解答
class Solution {
public int maximum69Number (int num) {
String s = String.valueOf(num);
return Integer.parseInt(s.replaceFirst("6","9"));
}
}
replaceFirst使用的是正則匹配，速度慢。
其他答案
public int maximum69Number(int num) {
char[] chars = Integer.toString(num).toCharArray();
for (int i = 0; i < chars.length; i++) {
if (chars[i] == '6') {
chars[i] = '9';
break;
}
}
return Integer.parseInt(new String(chars));
}
