2024/1/29~2024/2/4

本周主要学了bfs

简单的说,bfs就是用一个队列和结构体数组,或者多个数组,用队列对查找目标进行遍历,用其他数据结构对查找目标进行标记;

洛谷 P1331 海战

#include<bits/stdc++.h>
using namespace std;
using ll= long long;
constexpr int MOD=1000000007;

char c[1005][1005];
deque<pair<int,int>> dq;
int n,m,ans;
bool used[1005][1005];//是否走过
int dx[4]={-1,1,0,0},dy[4]={0,0,-1,1};//移动方向
bool check(int i,int j){
    int ok=0;
    if(c[i][j]=='#')ok++;
    if(c[i+1][j]=='#')ok++;
    if(c[i][j+1]=='#')ok++;
    if(c[i+1][j+1]=='#')ok++;
    if(ok==3)return false;
    return true;
}
void bfs(int a,int b){
    dq.push_back({a, b});

    while(!dq.empty()){
        auto [x,y]=dq.front();
        for(int i{0};i<4;i++){
            int xx=x+dx[i],yy=y+dy[i];
            if((!used[xx][yy])&&c[xx][yy]=='#'){
                dq.push_back({xx, yy});
               used[xx][yy]=true;
                //auto [x,y]=dq.front();
                //cout<<x<<" "<<y<<"\n";
            }
        }
        dq.pop_front();
    }
}
int main(){
    cin>>n>>m;

    for(int i{0};i<n;i++){
        for(int j{0};j<m;j++)cin>>c[i][j];
    }
    for(int i{0};i<n-1;i++){
        for(int j{0};j<m-1;j++){
            if(!check(i,j)){
                cout<<"Bad placement.";
                return 0;
            }
        }
    }
    for(int i{0};i<n;i++){
        for(int j{0};j<m;j++){
            if(c[i][j]=='#'&&(!used[i][j])){

                ans++;used[i][j]=true;
                bfs(i,j);
            }
        }
    }

    cout<<"There are "<<ans<<" ships.\n";

}

洛谷 B3625 迷宫寻路

#include<bits/stdc++.h>
using namespace std;
using ll= long long;
constexpr int MOD=1000000007;

char c[1005][1005];
deque<pair<int,int>> dq;
int n,m,ans;
bool used[1005][1005];//是否走过
int dx[4]={-1,1,0,0},dy[4]={0,0,-1,1};//移动方向

void bfs(int a,int b){
    dq.push_back({a, b});

    while(!dq.empty()){
        auto [x,y]=dq.front();
        for(int i{0};i<4;i++){
            int xx=x+dx[i],yy=y+dy[i];
            if((!used[xx][yy])&&c[xx][yy]=='.'){
                dq.push_back({xx, yy});
               used[xx][yy]=true;
                //auto [x,y]=dq.front();
                //cout<<x<<" "<<y<<"\n";
            }
        }
        dq.pop_front();
    }
}
int main(){
    cin>>n>>m;

    for(int i{0};i<n;i++){
        for(int j{0};j<m;j++)cin>>c[i][j];
    }
    bfs(0,0);
    //for(int i{0};i<n;i++){
    //    for(int j{0};j<m;j++){
    //        if(c[i][j]=='.'&&(!used[i][j])){
    //            ans++;used[i][j]=true;
    //            bfs(i,j);
    //        }
    //    }
    //}

    if(used[n-1][m-1]){cout<<"Yes";}
    else cout<<"No";
}

Wiki下象棋

题目链接:https://ac.nowcoder.com/acm/contest/74679/E

bfs搜两下就行了

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


int fx[8] = {-1, 1, 0, 0, -1, 1, -1, 1};
int fy[8] = {0, 0, -1, 1, -1, -1, 1, 1};

const int mod = 1000000007;
const int N = 200005;
const double eps = 1e-6;

int dx[8] = {1, 1, -1, -1, 2, 2, -2, -2};
int dy[8] = {2, -2, 2, -2, 1, -1, 1, -1};
int bx[8] = {0, 0, 0, 0, 1, 1, -1, -1};
int by[8] = {1, -1, 1, -1, 0, 0, 0, 0};
int n, m;
bool vis[305][305], board[305][305];
int bfs1(int sx, int sy, int ex, int ey) {
  memcpy(vis, board, sizeof(vis));
  queue<pair<int, int> > q;
  q.push(make_pair(sx, sy));
  int cnt = 1, step = 0;
  vis[sx][sy] = true;
  while (!q.empty()) {
    int sum = 0;
    while (cnt--) {
      auto [x, y] = q.front();
      q.pop();
      if (x == ex && y == ey) return step;
      for (int i = 0; i < 8; ++i) {
        int fx = x + dx[i], fy = y + dy[i];
        if (fx < 1 || fy < 1 || fx > n || fy > m || vis[fx][fy]) continue;
        q.push(make_pair(fx, fy));
        vis[fx][fy] = true;
        ++sum;
      }
    }
    ++step;
    cnt = sum;
  }
  return -1;
}
int bfs2(int sx, int sy, int ex, int ey) {
  memcpy(vis, board, sizeof(vis));
  queue<pair<int, int> > q;
  q.push(make_pair(sx, sy));
  int cnt = 1, step = 0;
  vis[sx][sy] = true;
  while (!q.empty()) {
    int sum = 0;
    while (cnt--) {
      auto [x, y] = q.front();
      q.pop();
      if (x == ex && y == ey) return step;
      for (int i = 0; i < 8; ++i) {
        int fx = x + dx[i], fy = y + dy[i];
        if (fx < 1 || fy < 1 || fx > n || fy > m || vis[fx][fy] ||
            board[x + bx[i]][y + by[i]])
          continue;
        q.push(make_pair(fx, fy));
        vis[fx][fy] = true;
        ++sum;
      }
    }
    ++step;
    cnt = sum;
  }
  return -1;
}

int main() {
  ios::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
  int T = 1;
  cin >> T;
  while (T--) {
    cin >> n >> m;
    int k, sx, sy, ex, ey;
    cin >> k >> sx >> sy >> ex >> ey;
    memset(board, false, sizeof(board));
    for (int i = 1; i <= k; i++) {
      int x, y;
      cin >> x >> y;
      board[x][y] = true;
    }
    cout << bfs1(sx, sy, ex, ey) << " " << bfs2(sx, sy, ex, ey) << endl;
  }
  return 0;
}

学了一些python,主要是使用Decimal库对高精度浮点数进行操作;
学历一些现代c++,union类似于c的struct,但是内存管理上更优秀(打比赛没啥用);