二分搜索

Binary Search

You are given a sequence of n integers S and a sequence of different q integers T. Write a program which outputs C, the number of integers in T which are also in the set S.

Input

In the first line n is given. In the second line, n integers are given. In the third line q is given. Then, in the fourth line, q integers are given.

Output

Print C in a line.

Constraints

• Elements in S is sorted in ascending order
• n ≤ 100000
• q ≤ 50000
• 0 ≤ an element in S ≤ 10⁹
• 0 ≤ an element in T ≤ 10⁹

Sample Input 1

5
1 2 3 4 5
3
3 4 1

Sample Output 1

3

Sample Input 2

3
1 2 3
1
5

Sample Output 2

0

Notes

本题是一种更加快捷的查找方法，但要求查找序列一定要是有序的序列。这样才可以对半砍来分，从而达到logn的复杂度。

代码如下：

    #include <iostream>  
    #include <cstdio>  
    #include <algorithm>  
    using namespace std;  
      
    const int maxn = 100000 + 5;  
      
    int n,sum = 0;  
    int a[maxn];  
      
    bool find(int key){  
      int l = 0,r = n;  
      while(l < r){  
        int mid = (l+r)>>1;  
        if(a[mid] < key){  
          l = mid+1;  
        }  
        else if(a[mid] > key){  
          r = mid;  
        }  
        else{  
          return true;  
        }  
      }  
      return false;  
    }  
      
    int main(){  
      scanf("%d",&n);  
      for(int i = 0;i < n; i++){  
        scanf("%d",&a[i]);  
      }  
      sort(a+1,a+n+1);  
      int q;  
      scanf("%d",&q);  
      for(int i = 0;i < q; i++){  
        int key;  
        scanf("%d",&key);  
        if(find(key)){  
          sum++;  
        }  
      }  
      printf("%d\n",sum);  
    }