75.Sort Colors

Given an array with n objects colored red, white or blue, sort them 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.

//最后排序结果，0放到最前面，2放到最后面

 

public void sortColors(int[] nums) {
  if (nums == null || nums.length < 2)
    return;
  int low = 0;
  int high = nums.length - 1;
  for (int i = low; i <= high;) {//注意i要和low，high比较，找到0时，i才加1，找到2时，i不动的
    if (nums[i] == 0) {
      swap(nums, i, low);
      low++;
      i++;//必须要有，否则输入是[0,0]的话，low一直自增nums[low]会越界
    } else if (nums[i] == 2) {
      swap(nums, i, high);
      high--;
    } else {
      i++;
    }
  }
}

private void swap(int[] nums, int i, int j) {
  int temp = nums[i];
  nums[i] = nums[j];
  nums[j] = temp;
}