POJ 2785 4 Values whose Sum is 0

枚举左边两个数的和以及右边两个数的和，用二分查找将其配对并计数。Hash的方法晚点再写。

 

/*Accepted 49208K 5188MS C++ 1146B 2012-05-04 23:56:30 */



#include<cstdio>

#include<cstring>

#include<cstdlib>

#include<algorithm>

using namespace std;

#define MAXN 4005



/*int cmp( const void *_p, const void *_q)

{

    int *p = ( int *)_p;

    int *q = ( int *)_q;

    return *p - *q;

}*/



int a[MAXN], b[MAXN], c[MAXN], d[MAXN];

int x[MAXN * MAXN], y[MAXN * MAXN];

int n, m, ans;



int bs( int num)

{

    int left, right, mid, i, cnt;

    left = 0, right = m;

    while( left < right)

    {

        mid = ( left + right) >> 1;

        if( num + y[mid] >= 0)

            right = mid;

        else left = mid + 1;

    }

    for( i = left, cnt = 0; i < m && y[i] + num == 0; i ++, cnt ++);

    return cnt;

}



int main()

{

    while( scanf( "%d", &n) == 1)

    {

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

            scanf( "%d%d%d%d", &a[i], &b[i], &c[i], &d[i]);

        m = 0;

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

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

            {

                x[m] = a[i] + b[j];

                y[m] = c[i] + d[j];

                m ++;

            }

        sort( x, x + m);

        sort( y, y + m);

        //qsort( x, m, sizeof x[0], cmp);

        //qsort( y, m, sizeof y[0], cmp);

        ans = 0;

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

            ans += bs( x[i]);

        printf( "%d\n", ans);

    }

    return 0;

}

 

用qsort超时了，百思不得其解！