题目描述
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?
解题思路
- 设置一个cnt从0开始
- 遍历这个序列，如果是0，与num[cnt]交换位置
- 然后重新遍历这个序列，如果是1，与num[cnt]交换位置
- 这样0,1就交换完了，剩下的就是2了
- 时间复杂度O(n)
暴力版本 报超时
C++代码
class Solution {
public:
void sortColors(vector<int>& nums) {
int cnt = 0;
for(int i = 0; i < nums.size(); i++){
if(nums[i] == 0){
swap(nums[i], nums[cnt]);
cnt++;
}
}
for(int i = 0; i < nums.size(); i++){
if(nums[i] == 1){
swap(nums[i], nums[cnt]);
cnt++;
}
}
}
};
