[leetcode] Sort Colors

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.

直观的想法又两种，一种是自己写快排吧，另一种是用计数排序，分别给出两种：

快排：

class Solution {
public:
void sortColors(int A[], int n) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
quick_sort(A,0,n-1);
}
int partition(int *array, int left , int right){
int pivot=array[left];
while(left<right){
for( ; right>left && array[right]>pivot ; right--);
array[left]=array[right];
for( ; left<right && array[left]<=pivot ; left++);
array[right]=array[left];
}
array[left]=pivot;
return left;
}
int quick_sort(int *array, int left , int right){
if(left<=right){
int p=partition(array,left,right);
quick_sort(array,left,p-1);
quick_sort(array,p+1,right);
}
}
};

计数排：

class Solution {
public:
void sortColors(int A[], int n) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
int count[3];
memset(count,0,sizeof(int)*3);
for(int i=0 ; i<n ; i++)
count[A[i]]++;
int k=0;
for(int i=0 ; i<n ; ){
if(count[k]==0){
k++;
continue;
}
else
count[k]--;
A[i++]=k;
}
}
};