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?
Solution:
class Solution {
public void sortColors(int[] nums) {
int l = 0;
int m = 0;
int h = nums.length - 1;
while (m <= h) {
if (nums[m] == 0) {
swap(nums, l, m);
l++; m++;
} else if (nums[m] == 1) {
m++;
} else if (nums[m] == 2) {
swap(nums, m, h);
h--;
}
}
}
void swap(int[] nums, int i, int j) {
int c = nums[i];
nums[i] = nums[j];
nums[j] = c;
}
}