## Question

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

n ≤ 10000

q ≤ 500

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

3 1 2

1

5

Sample Output 2

0

Sample Input 3

5

1 1 2 2 3

2

1 2

Sample Output 3

2

Notes

## Meaning

题目很简单，但是这里主要讲一个：线性搜索在引入标记之后，效率能提升常数倍。

## Coding

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#include<iostream> #include<cstdio> #include<stdio.h> using namespace std; //带有标记的线性搜索 int search(int A[],int n, int key) { int i = 0; A[n] = key;//标记搜索先给关键字放在末尾 while (A[i] != key) i++; return i != n; } int A[100005]; int main() { int n, q, key,sum=0; scanf("%d", &n); for (int i = 0; i < n; i++) scanf("%d", &A[i]); scanf("%d", &q); for (int i = 0; i < q; i++) { scanf("%d", &key); if (search(A, n, key)) sum++; } printf("%d\n", sum); } |

## Summary

向线性搜索种引入“标记”能够以将算法效率提升常数倍。

原始：

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LinearSearch() for i 从 0 到n-1 if A[i] 与key相等 return i returnNOT_FOUND |

改进后，给要查找的数放在数组末尾，用作标记。

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int search(int A[],int n, int key) { int i = 0; A[n] = key;//标记搜索先给关键字放在末尾 while (A[i] != key) i++; return i != n; } |

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