atcoder ABC 359-B题详解

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atcoder ABC 359-B题详解

Problem Statement

There are 2N people standing in a row, and the person at the i-th position from the left is wearing clothes of color Ai. Here, the clothes have N colors from 1 to N, and exactly two people are wearing clothes of each color.

Find how many of the integers i=1,2,…,N satisfy the following condition:

There is exactly one person between the two people wearing clothes of color i.

Constraints

2≤N≤100
1≤Ai≤N
Each integer from 1 through N appears exactly twice in A.
All input values are integers.

Input

The input is given from Standard Input in the following format:

N
A1 A2 … A2N
​

Output

Print the answer.

Sample Input 1

3
1 2 1 3 2 3

Sample Output 1

2
There are two values of i that satisfy the condition: 1 and 3.

In fact, the people wearing clothes of color 1 are at the 1st and 3rd positions from the left, with exactly one person in between.

Sample Input 2

2
1 1 2 2

Sample Output 2

0
There may be no i that satisfies the condition.

Sample Input 3

4
4 3 2 3 2 1 4 1

Sample Output 3

3

思路分析：

本题需要求解中间的那个数边上的两个数一样的个数，可以开vector直接来求解。

code：

#include <iostream>
#include <vector>
using namespace std;
vector<int>v;
int n;
int a;
int ans=0;
int main(){cin>>n;for(int i=0;i<2*n;i++){cin>>a;v.push_back(a);}for(int i=0;i<2*n;i++){if(v[i]==v[i+2]){ans++;}}cout<<ans;
}

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