POJ 3111 K Best 贪心 二分

Posted 2020-10-05 FriskyPuppy

　　题目链接： http://poj.org/problem?id=3111

　　题目描述： 

　　解题思路： 

　　代码： 这是我错的代码......一会儿回来改啊......一会儿回来可能会很沮丧

#include <iostream>
#include <cstdio>
#include <string>
#include <vector>
#include <cstring>
#include <iterator>
#include <cmath>
#include <algorithm>
#include <stack>
#include <deque>
#include <map>
#include <set>
#define lson l, m, rt<<1
#define rson m+1, r, rt<<1|1
#define mem0(a) memset(a,0,sizeof(a))
#define sca(x) scanf("%d",&x)
#define de printf("=======\n")
typedef long long ll;
using namespace std;

const double INF = 20000000.0;
const int maxn = 1e5+10;
int n, k;
struct node {
    double v;
    int index;
}y[maxn];
double v[maxn], w[maxn];
stack<int> ans;

int cmp( node n1, node n2 ) {
    return n1.v > n2.v;
}

bool ok( double x ) {
    for( int i = 0; i < n; i++ ) {
        y[i].v = v[i] - x*w[i];
        y[i].index = i+1;
    }
    double sum = 0;
    sort(y, y+k, cmp);
    for( int i = 0; i < k; i++ ) {
        sum += y[i].v;
    }
    if( sum >= 0 ) {
        while( !ans.empty() ) ans.pop();
        for( int i = 0; i < k; i++ ) {
            ans.push(y[i].index);
        }
    }
    return sum >= 0;
}

void solve() {
    double low = 0;
    double high = INF;
    for( int i = 0; i < 100; i++ ) {
        double m = (low + high) * 0.5;
        if( ok(m) ) {
            low = m;
        }
        else {
            high = m;
        }
    }
    stack<int> ans1;
    while( !ans.empty() ) {
        ans1.push(ans.top());
        ans.pop();
    }
    while( !ans1.empty() ) {
        int t = (int)ans1.size();
        if( t > 1 ) printf( "%d ", ans1.top() );
        else printf( "%d\n", ans1.top() );
        ans1.pop();
    }
}
int main() {
    while( scanf( "%d%d", &n, &k ) == 2 ) {
        for( int i = 0; i < n; i++ ) {
            scanf( "%lf%lf", v+i, w+i );
        }
        solve();
    }
    return 0;
}

View Code

　　思考：