排序算法之冒泡排序

 /*
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;
}