75. Sort Colors

Given an array with n objects colored red, white or blue, sort them in-place so that objects of the same color are adjacent, with the colors in the order red, white and blue.

Here, we will use the integers 0, 1, and 2 to represent the color red, white, and blue respectively.

Note: You are not suppose to use the library's sort function for this problem.

Example:

Input: [2,0,2,1,1,0]
Output: [0,0,1,1,2,2]

Follow up:

• A rather straight forward solution is a two-pass algorithm using counting sort.
  First, iterate the array counting number of 0's, 1's, and 2's, then overwrite array with total number of 0's, then 1's and followed by 2's.
• Could you come up with a one-pass algorithm using only constant space?

• class Solution {
      public void swap(int []nums, int l, int r) {
          int temp = nums[l];
          nums[l] = nums[r];
          nums[r] = temp;
      }
      public void sortColors(int[] nums) {
          int n = nums.length;
          int l = 0, r = n - 1;
          int i = 0;
          while (i >= l && i <= r && l <= r) {
              while (l <= r && nums[l] == 0) l++;
              while (l <= r && nums[r] == 2) r--;
              if (l > r) break;
              i = Math.max(i, l);
              if (nums[i] == 2) {
                  swap(nums, i, r--);
              } else if (nums[i] == 0) {
                  swap(nums, i, l++);
              } else {
                  i++;
              }
              
              
          }
          
      }
  }