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# 670.Maximum-Swap

## 题目描述

Given a non-negative integer, you could swap two digits at most once to get the maximum valued number. Return the maximum valued number you could get.
Example 1:
Input: 2736
Output: 7236
Explanation: Swap the number 2 and the number 7.
Example 2:
Input: 9973
Output: 9973
Explanation: No swap.
Note:
The given number is in the range [0, 108]

## 代码

### Approach #2 Greedy

class Solution {
public int maximumSwap(int num) {
char[] A = Integer.toString(num).toCharArray();
int[] last = new int[10];
for (int i = 0; i < A.length; i++) {
last[A[i] - '0'] = i;
}
for (int i = 0; i < A.length; i++) {
for (int d = 9; d > A[i] - '0'; d--) {
if (last[d] > i) {
char tmp = A[i];
A[i] = A[last[d]];
A[last[d]] = tmp;
return Integer.valueOf(new String(A));
}
}
}
return num;
}
}

### Approach #1 Brute Force

class Solution {
public int maximumSwap(int num) {
char[] A = Integer.toString(num).toCharArray();
char[] ans = Arrays.copyOf(A, A.length);
for (int i = 0; i < A.length; i++) {
for (int j = i+1; j < A.length; j++) {
char tmp = A[i];
A[i] = A[j];
A[j] = tmp;
for (int k = 0; k < A.length; k++){
if (A[k] != ans[k]){
if (A[k] > ans[k]) {
ans = Arrays.copyOf(A, A.length);
}
break;
}
}
A[j] = A[i];
A[i] = tmp;
}
}
return Integer.valueOf(new String(ans));
}
}