最大交换

/*
 * Problem: Given a non-negative integer, you can swap at most once two digits of the number to get the maximum possible value. 
 * Solution: Convert the number to a character array, then find the highest possible number by swapping two digits. 
 * - Use Java Streams to manage the manipulation of the number as an array of digits. 
 * - Find the maximum digit that can be swapped to increase the number.
 */
 
import java.util.stream.IntStream;
 
public class Solution {
    public int maximumSwap(int num) {
        char[] digits = Integer.toString(num).toCharArray();
        int n = digits.length;
        int[] maxIndex = IntStream.range(0, n).toArray();
 
        // Record the position of the max digit to the right of each digit
        IntStream.range(0, n - 1).forEach(i -> {
            maxIndex[i] = IntStream.range(i + 1, n).boxed()
                    .max((j1, j2) -> digits[j1] - digits[j2])
                    .orElse(i);
        });
 
        // Find the first position where a larger digit can be swapped
        int pos = IntStream.range(0, n)
                .filter(i -> digits[i] < digits[maxIndex[i]])
                .findFirst()
                .orElse(-1);
 
        if (pos != -1) {
            // Swap
            char temp = digits[pos];
            digits[pos] = digits[maxIndex[pos]];
            digits[maxIndex[pos]] = temp;
        }
 
        return Integer.parseInt(new String(digits));
    }
}