Array - 75. Sort Colors

1. 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]

• 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?

java：

``````class Solution {

public void sortColors(int[] nums) {
if (nums == null || nums.length <= 1) return;

int i = 0, j = 0, k= nums.length - 1;
while (j <= k) {
if (nums[j] == 0) {
swap(nums, i++, j++);
} else if (nums[j] == 1) {
j++;
} else {
swap(nums, j, k--);
}
}
}

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

Nothing just happens, it's all part of a plan.