{"id":34362,"date":"2024-11-01T09:27:17","date_gmt":"2024-11-01T09:27:17","guid":{"rendered":"http:\/\/atmokpo.com\/w\/?p=34362"},"modified":"2024-11-01T10:57:32","modified_gmt":"2024-11-01T10:57:32","slug":"c-coding-test-course-finding-cities-at-a-specific-distance-2","status":"publish","type":"post","link":"https:\/\/atmokpo.com\/w\/34362\/","title":{"rendered":"C++ Coding Test Course, Finding Cities at a Specific Distance"},"content":{"rendered":"

<\/p>\n

Hello, in this lecture, we will explore the process of solving algorithm problems using C++. We will tackle a problem called ‘Finding Cities at a Certain Distance’ through graph traversal. This problem is one of the frequent topics in coding tests and can be solved using graph traversal techniques like BFS (Breadth-First Search) or DFS (Depth-First Search).<\/p>\n

Problem Description<\/h2>\n

The requirements of the problem are as follows:<\/p>\n

\n

There are N cities. Each city is connected to one another, and there are roads. The road connecting two cities A and B may be one-way. Given the number of cities N, the number of roads M, and the distance K, write a program that outputs the numbers of cities that are at distance K. If there are no such cities, print -1. There are no multiple roads connecting two cities A and B, and all roads are one-way.<\/p>\n<\/blockquote>\n

Input Format<\/h2>\n

The first line contains the number of cities N, the number of roads M, and the distance K. From the second line onward, M lines contain information about the roads, with each road represented by two integers A and B indicating that there is a one-way road from A to B.<\/p>\n

Output Format<\/h2>\n

You should output the number of the city at distance K, and if there are no such cities, you should output -1.<\/p>\n

Example Input<\/h3>\n
\n    4 4 2\n    1 2\n    1 3\n    2 3\n    2 4\n    <\/pre>\n
Example Output<\/h3>\n
\n    4\n    <\/pre>\n
Problem-Solving Process<\/h2>\n
We will solve the problem using a graph. We’ll treat each city as a vertex and the roads as edges to build the graph. Let’s go through the steps to solve the problem.<\/p>\n
1. Representing the Graph<\/h3>\n
In the first step, we will represent the graph using an adjacency list. The adjacency list is a format that stores a list of connected vertices for each vertex. This allows us to easily verify the connection relationships between cities.<\/p>\n
2. Searching Using BFS<\/h3>\n
We will use the BFS (Breadth-First Search) algorithm to search for cities at a certain distance. BFS is an algorithm that starts from one vertex and explores all its adjacent vertices level by level, which is suitable for finding nodes at a specific distance.<\/p>\n
3. Storing and Handling Results<\/h3>\n
We will collect all the city numbers that correspond to distance K and output them. Additionally, we will set it to output -1 if there are no cities at distance K.<\/p>\n
Implementation Code<\/h2>\n
Below is the code implemented in C++. This code allows us to solve the problem.<\/p>\n
\n#include <iostream>\n#include <vector>\n#include <queue>\n#include <algorithm>\n\nusing namespace std;\n\nint main() {\n    int N, M, K;\n    cin >> N >> M >> K;\n\n    vector<vector<int>> graph(N + 1);\n    for (int i = 0; i < M; i++) {\n        int A, B;\n        cin >> A >> B;\n        graph[A].push_back(B);\n    }\n\n    vector<int> distance(N + 1, -1);\n    queue<int> q;\n\n    \/\/ Set the starting city 1 to distance 0\n    distance[1] = 0;\n    q.push(1);\n\n    while (!q.empty()) {\n        int current = q.front();\n        q.pop();\n\n        for (int next : graph[current]) {\n            if (distance[next] == -1) {\n                distance[next] = distance[current] + 1;\n                q.push(next);\n            }\n        }\n    }\n\n    vector<int> result;\n    for (int i = 1; i <= N; i++) {\n        if (distance[i] == K) {\n            result.push_back(i);\n        }\n    }\n\n    if (result.empty()) {\n        cout << -1 << endl;\n    } else {\n        sort(result.begin(), result.end());\n        for (int city : result) {\n            cout << city << endl;\n        }\n    }\n\n    return 0;\n}\n    <\/pre>\n
Conclusion<\/h2>\n
In this lecture, we learned about graph traversal techniques through the problem of ‘Finding Cities at a Certain Distance’ and explored how to solve the problem using BFS. Problems like this are frequently encountered in algorithm interviews, so it’s important to practice enough to develop problem-solving skills. In the next lecture, we will tackle another algorithm problem. Thank you!<\/p>\n
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Hello, in this lecture, we will explore the process of solving algorithm problems using C++. We will tackle a problem called ‘Finding Cities at a Certain Distance’ through graph traversal. 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