Uva live 4043 Ants（ KM+简单的计算几何）

一定要清楚的一个问题，就是：（如图）两条黑色的线的和一定小于蓝色的和，但是平方的和之间就不一定是这个关系了！

代码：

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <cmath>
using namespace std;

const double INF = 0x7fffffff;
const double eps = 1e-9;
const int N = 110;
int n;
double w[N][N], lx[N], ly[N];
int l[N], r[N];
int wx[N], wy[N], bx[N], by[N];
bool S[N], T[N];

bool eq( double x, double y ) {
    return fabs ( x - y ) < eps;
}
bool match( int i )
{
    S[i] = true;
    for ( int j = 1; j <= n; ++j ) if ( eq( lx[i] + ly[j], w[i][j] ) && !T[j] ) {
        T[j] = true;
        if ( !l[j] || match(l[j]) ) {
            l[j] = i;
            //r[i] = j;
            return true;
        }
    }
    return false;
}
void update()
{
    double a = INF;
    for ( int i = 1; i <= n; ++i ) if ( S[i] ) 
        for ( int j = 1; j <= n; ++j ) if ( !T[j] ) 
            a = min( a, lx[i]+ly[j]-w[i][j] );
    for ( int i = 1; i <= n; ++i ) {
        if ( S[i] ) lx[i] -= a;
        if ( T[i] ) ly[i] += a;
    }
}
void KM()
{
    //memset(l, 0, sizeof(l));
    //memset(r, 0, sizeof(r));
    for ( int i = 1; i <= n; ++i ) {
        l[i] = lx[i] = ly[i] = 0;
        for ( int j = 1; j <= n; ++j ) 
            lx[i] = max( lx[i], w[i][j] );
    }
    for ( int i = 1; i <= n; ++i ) {
        for(;;) {
            for ( int j = 1; j <= n; ++j ) S[j] = T[j] = 0;
            if ( match(i) ) break; 
            else update();
        }
    }
}
int main()
{
    bool first = false;
    while ( scanf("%d", &n) != EOF ) {
        if ( first ) printf("\n");
        first = true;
        for ( int i = 1; i <= n; ++i ) scanf("%d%d", &wx[i], &wy[i]);
        for ( int i = 1; i <= n; ++i ) scanf("%d%d", &bx[i], &by[i]);
        for ( int i = 1; i <= n; ++i ) 
            for ( int j = 1; j <= n; ++j ) 
                w[j][i] = -sqrt((double)(wx[i]-bx[j])*(wx[i]-bx[j])+(double)(wy[i]-by[j])*(wy[i]-by[j]));
        KM();
        for ( int i = 1; i <= n; ++i ) printf("%d\n", l[i]);
    }
}