110.字符串接龙

110. 字符串接龙 (kamacoder.com)

#include<iostream>
#include<vector>
#include<unordered_set>
#include<unordered_map>
#include<string>
#include<queue>

using namespace std;

int main(){
    int n = 0;
    cin >> n;
    string beginStr, endStr, strMid;
    cin >> beginStr >> endStr;
    unordered_set<string> strList;
    for(int i = 0; i < n; i++){
        cin >> strMid;
        strList.insert(strMid);
    }
    unordered_map<string, int> strMap;  // 访问到字符串str1时的长度
    queue<string> strQue;
    strQue.push(beginStr);
    strMap[beginStr] = 1;
    while(!strQue.empty()){
        string strFront = strQue.front();
        strQue.pop();
        int strSize = strFront.size();
        for(int i = 0; i < strSize; i++){
            string prevStr = strFront;
            for(int j = 0; j < 26; j++){
                strFront[i] = j + 'a';
                if(strFront == endStr){
                    cout << strMap[prevStr] + 1 << endl;
                    return 0;
                }
                if(strList.count(strFront) && !strMap.count(strFront)){  
                    // 要求有且没被用过，可以保证每次到str的长度是最短的
                    strMap[strFront] = strMap[prevStr] + 1; 
                    strQue.push(strFront);
                }
            }
            strFront = prevStr;
        }
    }
    cout << 0;
    return 0;
    
}

105.有向图的完全可达性

105. 有向图的完全可达性 (kamacoder.com)

#include <iostream>
#include <vector>
#include <queue>
#include <unordered_set>

using namespace std;

int main()
{
    int n = 0, k = 0;
    cin >> n >> k;
    vector<queue<int>> map(n + 1);
    for (int i = 0; i < k; i++)
    {
        int start = 0, end = 0;
        cin >> start >> end;
        map[start].push(end);
    }
    unordered_set<int> record;
    queue<int> que;
    que.push(1);
    record.insert(1);
    while (!que.empty())
    {
        int curTop = que.front();
        que.pop();
        while (!map[curTop].empty())
        {
            int queTop = map[curTop].front();
            map[curTop].pop();
            if (record.count(queTop))  // 去重
            {
                continue;
            }
            record.insert(queTop);
            que.push(queTop);
        }
    }
    for (int i = 2; i <= n; i++)
    {
        if (!record.count(i))
        {
            cout << -1 << endl;
            return 0;
        }
    }
    cout << 1 << endl;
    return 0;
}

106.岛屿的周长

106. 岛屿的周长 (kamacoder.com)

#include<iostream>
#include<vector>

using namespace std;
int ans = 0; // 记录周长
int dir[4][2] = {1, 0, 0, 1, -1, 0, 0, -1};

void dfs(int x, int y, vector<vector<int>> &visited, vector<vector<int>> &island, int n, int m){
    visited[x][y] = 1;
    for(int i = 0; i < 4; i++){
        int nextX = x + dir[i][0];
        int nextY = y + dir[i][1];
        if(nextY < 0 || nextX < 0 || nextY >= m || nextX >= n || island[nextX][nextY] == 0){
            ans++;
            continue;
        }
        if(visited[nextX][nextY] == 0){
            dfs(nextX, nextY, visited, island, n, m);
        }
    }
}

int main(){
    int n = 0, m = 0;
    cin >> n >> m;
    vector<vector<int>> island(n, vector<int>(m));
    vector<vector<int>> visited(n, vector<int>(m));
    for(int i = 0;i < n; i++){
        for(int j = 0; j < m; j++){
            cin >> island[i][j];
        }
    }
    for(int i = 0; i < n; i++){
        for(int j = 0; j < m; j++){
            if(island[i][j] != 0 && visited[i][j] == 0)
            dfs(i, j, visited, island, n, m);
        }
    }
    cout << ans << endl;
    return 0;
}