75. Sort Colors（第三周）

Description

Sort Colors - LeetCode

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.

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 an one-pass algorithm using only constant space?

Input:

[1, 0, 0, 2]

Output:

[0, 0, 1, 2]

Solution

从这个题目一共就只有三种颜色可以很快的想到桶排序。于是我就有以下思路：先定义三个变量来分别记录0、1、和2的数量，然后在根据0、1、2的数量来按顺序填充回原来的数组即可。

代码如下

Source Code

submission

class Solution {
public:
void sortColors(vector<int>& nums) {
int red(0);
int white(0);
int blue(0);
for (auto iter = nums.begin(); iter != nums.end(); iter++) {
switch (*iter) {
case 0:
red++;
break;
case 1:
white++;
break;
case 2:
blue++;
break;
default:
break;
}
}
int cnt(0);
while (red--) {
nums[cnt++] = 0;
}
while (white--) {
nums[cnt++] = 1;
}
while (blue--) {
nums[cnt++] = 2;
}
}
};

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