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
代码语言：javascript复制#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("%dn", 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：
代码语言：javascript复制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。
代码语言：javascript复制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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转载请注明原文链接：Linear Search
