670. Maximum Swap

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:

1. The given number is in the range [0, 108]

670. Maximum Swap
struct Solution;

impl Solution {
fn maximum_swap(num: i32) -> i32 {
let mut s: Vec<char> = num.to_string().chars().collect();
let n = s.len();
let mut last: Vec<usize> = vec![0; 10];
for i in 0..n {
last[(s[i] as u8 - b'0') as usize] = i;
}
for i in 0..n {
let d = (s[i] as u8 - b'0') as usize;
for j in (d + 1..10).rev() {
if last[j] > i {
s.swap(i, last[j]);
return s.into_iter().collect::<String>().parse::<i32>().unwrap();
}
}
}
num
}
}

#[test]
fn test() {
let num = 2736;
let res = 7236;
assert_eq!(Solution::maximum_swap(num), res);
let num = 9973;
let res = 9973;
assert_eq!(Solution::maximum_swap(num), res);
let num = 9973;
let res = 9973;
assert_eq!(Solution::maximum_swap(num), res);
let num = 19;
let res = 91;
assert_eq!(Solution::maximum_swap(num), res);
}