Một bài sử dụng cấu trúc dữ liệu hay (Mảng hai chiều)

Đề bài:

A country X consists of N cities numbered 0 through $N-1$. The map of this country can be represented as a cycle — for each valid i, city i has exactly two neighboring cities $(i+1)\mathrm{\%}N$ and $(i-1+N)\mathrm{\%}N$.
The cities in the country are broadly categorized into different types. For each valid i, the type of city i is denoted by $A_i$.
A person called Suarez wants to travel between some pairs of the cities. You are given Q queries. In each query, Suarez wants to travel from city number Y to a city of type Z. Also, he wants to travel only in a given direction along the cycle.
The direction is represented by a letter — L or R. If it's L, Suarez may only move from city i to city $(i-1+N)\mathrm{\%}N$ for each valid i. If it's R, he may only move from city i to city $(i+1)\mathrm{\%}N$.
You need to find the minimum number of steps Suarez needs to take to reach a city of type Z if he starts moving from city Y in the given direction (he can take zero steps). In one step, Suarez can move from his current city to a neighboring city.
If Suarez can never reach a city of type Z for a given query, print 1 instead.
Constraints

• $1\le N\le 3,000$
• $1\le Q\le 500,000$
• $0\le Y<N$
• $1\le A_i,Z\le 200,000$

Input format
The first line of the input contains two space-separated integers N and Q. The next line contains N space-separated integers, where the i-th of these integers represents $A_i$.
Each of the following Q lines describes a query in the format $YZD$, where Y is an integer denoting the number of the starting city, Z is an integer denoting the type of a target city and D is a letter ('L' or 'R') denoting the direction along the cycle.
Output format
For each query, print a single line containing one integer — the answer to the query.

SAMPLE INPUT

 

3 4
1 2 3
0 1 L
1 3 L
2 1 R
1 5 L

SAMPLE OUTPUT

 

0
2
1
-1

Explanation

For the first query, Suarez is already standing in a city of the required type, hence 0 steps taken.
For the second query, Suarez will take the path 1 -> 0 -> 2, hence 2 steps taken.
For the third query, Suarez will take the path 2 -> 0, hence 1 step taken.
For the fourth query, there is no city of type 5, so the answer is 1.

Lời giải:

#include<bits/stdc++.h>
using namespace std;
int main(){
   ios_base::sync_with_stdio(false);
   cin.tie(NULL);
   cout.tie(NULL);
   int n,q;
   cin>>n>>q;
   vector<int> v[200002];
   int arr[n];
   for(int i=0;i<n;i++){
      cin>>arr[i];
      v[arr[i]].push_back(i);
   }
   while(q--){
      int y,z;
      char d;
      cin>>y>>z>>d;
      int ans=INT_MAX;
      if(v[z].size()==0){
        cout<<"-1\n";
      }
      else{
        if(d=='L'){
            for(int i=0;i<v[z].size();i++)
                if(v[z][i]<=y) ans=min(ans,abs(v[z][i]-y));
            else
                ans=min(ans,abs(n-abs(v[z][i]-y)));
        }
        else{
            for(int i=0;i<v[z].size();i++)
                 if(v[z][i]>=y)
                   ans=min(ans,abs(v[z][i]-y));
            else
                ans=min(ans,abs(n-abs(v[z][i]-y)));
        }
        cout<<ans<<endl;
      }
   }
   return 0;
}