poj1328Radar Installation--貪心

代碼如下：

#include <cstdio>
#include <iostream>
#include <cstring>
#include <cctype>
#include <cmath>
#include <algorithm>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <cstdlib>
#include <vector>
#define ll long long
#define maxn 1010
using namespace std;
double x[maxn], y[maxn];
int main()
{
    int n, d, a, b, w = 1;

    while ( ~scanf( "%d%d", &n, &d) && ( d || n)){
            bool fg = false;
        for ( int i = 0; i < n; i++){
            scanf( "%d%d", &a, &b);
            if ( b > d || b < 0)
                fg = true;
            if ( !fg){
                x[i] = a - sqrt( 1.0 * d * d - b * b);
                y[i] = a + sqrt( 1.0 * d * d - b * b);
            }
        }
        printf( "Case %d: ", w++);
        if ( fg){
            printf( "-1\n");
        }
        else{
            for ( int i = 0; i < n - 1; i++){
                int k = i;
                for ( int j = i + 1; j < n; j++){
                    if ( y[k] - y[j] > 1e-8){
                        k = j;
                    }
                    else if ( fabs( y[j] - y[k]) < 1e-8 && x[j] - x[k] > 1e-8){
                        k = j;
                    }
                }
                if ( k != i){
                    swap( x[i], x[k]);
                    swap( y[i], y[k]);
                }
            }
            double z = y[0];
            int c = 1;
            for ( int i = 1; i < n; i++){
                if ( x[i] - z > 1e-8){
                    z = y[i];
                    c++;
                }
            }
            printf( "%d\n", c);
        }
    }
    return 0;
}