1095. Maximum Swap —— Weekly Challenge

题目限定输入是[0, 10^8]，因而不用考虑负数或者越界情况，算是减小了难度。

 public class Solution {
     /**
      * @param num: a non-negative intege
      * @return: the maximum valued number
      */
     public int maximumSwap(int num) {
         // Write your code here
         char[] numArrays = String.valueOf(num).toCharArray();
         if (numArrays.length < 2) {
             return num;
         }

         //第一个递增点:
         int firstHeigerPoint = 0;
         for (int i = 0; i < numArrays.length - 1; i++) {
             if (numArrays[i] < numArrays[i + 1]) {
                 firstHeigerPoint = i + 1;
                 break;
             }
         }

         if (firstHeigerPoint == 0) {
             return num;
         }

         //找到递增点后的最大值(如有相等情况取低位，因而更新条件是numArrays[j] >= max)
         int max = numArrays[firstHeigerPoint];
         int maxPoint = firstHeigerPoint;
         for (int j = firstHeigerPoint; j < numArrays.length; j++) {
             if (numArrays[j] >= max) {
                 max = numArrays[j];
                 maxPoint = j;
             }
         }

         //找到第一个更小的高位
         int toSwapIndex = firstHeigerPoint-1;
         for (int i = 0; i <= firstHeigerPoint - 1; i++) {
             if (numArrays[i] < max) {
                 toSwapIndex = i;
                 break;
             }
         }

         char temp = numArrays[toSwapIndex];
         numArrays[toSwapIndex] = numArrays[maxPoint];
         numArrays[maxPoint] = temp;

         return Integer.parseInt(new String(numArrays));
     }
 }