counting sort 计数排序

//counting sort 计数排序

//参考算法导论8.2节

#include<cstdio>

#include<cstring>

#include<algorithm>

#include<cassert>

using namespace std;

const int k=5;

const int n=7;

int a[n]={5, 5, 1, 2 , 5, 4, 1};

int b[n];

int c[k+1];

int main()

{

    int maxn=0;

    memset(c, 0, sizeof c);

    for(int i=0;i<n;i++)

    {

        c[a[i]]++;

        maxn=max(maxn, a[i]);

    }

    assert(maxn<=k);
//统计<=i的个数, c[i]就是最终i要放置的位置

    for(int i=1;i<=maxn;i++)

    {

        c[i]+=c[i-1];

    }

    for(int i=0;i<=maxn;i++)

        printf("%d ", c[i]);

    printf("\n");
for(int i=n-1;i>=0;i--)

    {

        b[c[a[i]] - 1]=a[i];//从0开始

        --c[a[i]];

    }
for(int i=0;i<n;i++)

        printf("%d ", b[i]);

    printf("\n");

    return 0;

}

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