LightOJ 1088 - Points in Segments 二分

Posted 2020-08-25 ( m Lweleth)

http://www.lightoj.com/volume_showproblem.php?problem=1088

 

题意：给出N个点，Q个查询，问在区间内的点数有多少个。

思路：直接在线二分，注意边界问题

 

 

/** @Date    : 2016-12-17-19.03
  * @Author  : Lweleth ([email protected])
  * @Link    : https://github.com/
  * @Version :
  */
#include<bits/stdc++.h>
#define LL long long
#define PII pair
#define MP(x, y) make_pair((x),(y))
#define fi first
#define se second
#define PB(x) push_back((x))
#define MMG(x) memset((x), -1,sizeof(x))
#define MMF(x) memset((x),0,sizeof(x))
#define MMI(x) memset((x), INF, sizeof(x))
using namespace std;

const int INF = 0x3f3f3f3f;
const int N = 1e5+20;
const double eps = 1e-8;

int a[N];
int query(int x, int y, int n)//二分细节阿阿阿 边界问题
{
    int p1 = -1, p2 = -1;

    int l = 0, r = n - 1;
    while(l <= r)
    {
        int mid = (l + r) >> 1;
        //cout << "l1:" < a[mid])
            l = mid + 1;
    }

    l = 0, r = n - 1;
    while(l <= r)
    {
        int mid = (l + r) >> 1;
        //cout << "l2:" <= a[mid])
            l = mid + 1, p2 = mid;
    }
    if(!(~p1) || !(~p2))//
        return 0;
    else
        return p2 - p1 + 1;
}


int main()
{
    int T;
    int cnt = 0;
    cin >> T;
    while(T--)
    {
        int n, q;
        scanf("%d%d", &n, &q);
        for(int i = 0; i < n; i++)
            scanf("%d", a + i);

        printf("Case %d:\n", ++cnt);
        while(q--)
        {
            int x, y;
            scanf("%d%d", &x, &y);
            int ans = query(x, y, n);
            printf("%d\n", ans);
        }
    }
    return 0;
}