Sort Colors

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.

两种思路，一种遍历计数，一种三指针交换

class Solution {public:    void sortColors(int a[], int n) {        int p,i,m;        p=0,m=0;        for(i=0;i<n;i++)        {            if(a[i]==0) p++;            if(a[i]==1) m++;        }        for(i=0;i<p;i++)        {            a[i]=0;        }        for(;i<p+m;i++)        {            a[i]=1;        }        for(;i<n;i++)        {            a[i]=2;        }  }};

class Solution {public:void sortColors(int a[], int n) {        int i = -1;        int j = -1;        int k = -1;        for(int p = 0; p < n; p ++)        {            if(a[p] == 0)            {                a[++k] = 2;                   a[++j] = 1;                    a[++i] = 0;               }            else if(a[p] == 1)            {                a[++k] = 2;                a[++j] = 1;            }            else                a[++k] = 2;        }    }};

class Solution {public:    void swap(int a[],int m,int n)    {        int tem=a[m];        a[m]=a[n];        a[n]=tem;    }    void sortColors(int a[], int n) {        int l,cur,r;        l=0,r=n-1,cur=n-1;        while(cur>=l)        {            if(a[cur]==0)            {                swap(a,cur,l);                l++;            }            else if(a[cur]==2)            {                swap(a,cur,r);                r--;                cur--;            }            else            cur--;        }                    }};