csp202012

期末预测之安全指数

实现

#include<bits/stdc++.h>
using namespace std;
int n;
int a,b;
int ans;
int main()
{
    
    
    cin>>n;
    while(n--)
    {
    
    
        scanf("%d%d",&a,&b);
        ans+=(a*b);
    }
    cout<<max(0,ans);
}

期末预测之最佳阈值

思路

维护两个前缀和数组，分别是前i个中有多少个0和多少个1。

实现

#include<bits/stdc++.h>
#define x first
#define y second

using namespace std;

typedef pair<int, int> PII;
const int N = 100010;

int n;
PII q[N];
int s[2][N];

int main()
{
    
    
    scanf("%d", &n);
    for (int i = 1; i <= n; i ++ ) scanf("%d%d", &q[i].x, &q[i].y);
    sort(q + 1, q + n + 1);
    for (int i = 0; i < 2; i ++ )
        for (int j = 1; j <= n; j ++ )
            s[i][j] = s[i][j - 1] + (q[j].y == i);

    int cnt = -1, res;
    for (int i = 1; i <= n; i ++ )
    {
    
    
        int t = s[0][i - 1] + s[1][n] - s[1][i - 1];
        if (t >= cnt) cnt = t, res = q[i].x;
        while (i + 1 <= n && q[i + 1].x == q[i].x) i ++ ;
    }
    printf("%d\n", res);
    return 0;
}