排序算法之冒泡排序

题目传送门

/*
    BubbleSort_2(),_3()为优化版
    用zstu3539题目来验证算法的正确性
*/
#include <cstdio>
#include <iostream>
#include <algorithm>
#include <ctime>
#include <cstdlib>
using namespace std;

const int maxn = 1000000 + 10;
const int INF = 0x3f3f3f3f;
int a[maxn];

void BubbleSort(int *a, int n)
{
    for (int i=1; i<=n-1; ++i)
    {
        for (int j=1; j<=n-i; ++j)
        {
            if (a[j] > a[j+1])    swap (a[j], a[j+1]);
        }
    }
}

void BubbleSort_2(int *a, int n)        //若不进行交换，已排好序，算法结束
{

    for (int i=1; i<=n-1; ++i)
    {
        int pos = 0;
        for (int j=1; j<=n-i; ++j)
        {
            if (a[j] > a[j+1])
            {
                swap (a[j], a[j+1]);
                pos = j;
            }
        }
        if (pos == 0)    break;
    }
}

void BubbleSort_3(int *a, int n)        //一次冒泡得到最大值和最小值，排序次数几乎减少一半
{
    int l = 1, r = n;
    while (l < r)
    {
        for (int i=l; i<r; ++i)        //正向冒泡
        {
            if (a[i] > a[i+1])    swap (a[i], a[i+1]);
        }
        --r;
        for (int i=r; i>l; --i)        //反向冒泡
        {
            if (a[i] < a[i-1])    swap (a[i], a[i-1]);
        }
        ++l;
    }
}

int main(void)
{
    //freopen ("rand_small.in", "r", stdin);
    int n;

    while (scanf ("%d", &n) != EOF)
    {
        if (n == 0)
            continue;
        for (int i=1; i<=n; ++i)
        {
            scanf ("%d", &a[i]);
        }
    
        BubbleSort (a, n);
        //BubbleSort_2 (a, n);
        //BubbleSort_3 (a, n);

        bool flag = true;
        for (int i=1; i<=n; ++i)
        {
            if (flag)
            {
                printf ("%d", a[i]);
                flag = false;
            }
            else
                printf (" %d", a[i]);
        }
        puts ("");
    }

    return 0;
}