MaximumSwap.java

package array;

/**
 * Created by gouthamvidyapradhan on 10/12/2017.
 * 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]

 Solution O(n): Create a array of digit index. Iterate through the digits starting from left and in each iteration
 check if there is any digit which is greater than the current digit and appearing after the current index, if found
 then swap and return the new integer.
 */
public class MaximumSwap {

    public static void main(String[] args) throws Exception{
        System.out.println(new MaximumSwap().maximumSwap(2736));
    }

    public int maximumSwap(int num) {
        int[] D = new int[10];
        char[] A = String.valueOf(num).toCharArray();
        for(int i = 0; i < A.length; i ++){
            D[A[i] - '0'] = i;
        }

        boolean found = false;

        for(int i = 0; i < A.length; i ++){
            int digit = A[i] - '0';
            for(int j = 9; j > digit; j--){
                if(D[j] > i){
                    char temp = A[i];
                    A[i] = (char)(j + '0');
                    A[D[j]] = temp;
                    found = true;
                    break;
                }
            }
            if(found) break;
        }

        return Integer.parseInt(String.valueOf(A));
    }

}