dfs由易到难

P1162 填涂颜色

bfs大致思路就是先把起始点放入队列中，这道题从四周的0为起点，并设置一个标记函数，最后遍历就行

#include<bits/stdc++.h>
using namespace std;

const int N=35;
int n,g[N][N],visited[N][N];
int dx[4]={1,0,-1,0},dy[4]={0,1,0,-1};

void bfs(){
    queue<pair<int,int>> q;
    for(int i=1;i<=n;i++){
        if(g[1][i]==0){
            q.push({1,i});
            visited[1][i]=1;
        }
        if(g[n][i]==0){
            q.push({n,i});
            visited[n][i]=1;
        }
        if(g[i][1]==0){
            q.push({i,1});
            visited[i][1]=1;
        }
        if(g[i][n]==0){
            q.push({i,n});
            visited[i][n]=1;
        }
    }
    while(!q.empty()){
        auto [x,y]=q.front();
        q.pop();
        for(int i=0;i<4;i++){
            int nx=x+dx[i],ny=y+dy[i];
            if(nx<1||ny<1||nx>n||ny>n) continue;
            if(g[nx][ny]==1||visited[nx][ny]) continue;
            visited[nx][ny]=1;
            q.push({nx,ny});
        }
    }
}
int main(){
    cin>>n;
    for(int i=1;i<=n;i++)
        for(int j=1;j<=n;j++)
                cin>>g[i][j];
    bfs();
    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            if(g[i][j]==0&&!visited[i][j]) cout<<"2 ";
            else cout<<g[i][j]<<" ";
        }
        cout<<endl;
    }
    return 0;
}

P1135 奇怪的电梯

#include<bits/stdc++.h>
using namespace std;
const int N = 205;
int n, a, b;
int g[N];
bool visited[N];
int bfs(){
    queue<pair<int,int>> q;
    q.push({a, 0});
    visited[a]=true;
    while(!q.empty()){
        auto [floor, steps]=q.front();
        q.pop();
        
        if(floor==b){
            return steps;
        }

        int up=floor+g[floor];
        if(up<=n&&!visited[up]){
            visited[up]=true;
            q.push({up,steps+1});
        }
        int down=floor-g[floor];
        if(down>=1&&!visited[down]){
            visited[down] =true;
            q.push({down,steps+1});
        }
    }
    return -1;
}
int main() {
    cin>>n>>a>>b;
    for(int i=1;i<=n;i++) {
        cin>>g[i];
    }
    int result=bfs();
    cout<<result<<endl;
    return 0;
}