0075. Sort Colors

# 75. Sort Colors#

## 题目 #

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 1:

``````
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?

## 代码 #

``````
package leetcode

func sortColors(nums []int) {
if len(nums) == 0 {
return
}

r := 0
w := 0
b := 0 // label the end of different colors;
for _, num := range nums {
if num == 0 {
nums[b] = 2
b++
nums[w] = 1
w++
nums[r] = 0
r++
} else if num == 1 {
nums[b] = 2
b++
nums[w] = 1
w++
} else if num == 2 {
b++
}
}
}

``````

Sep 6, 2020