Table of contents

• Problem
  • Input
  • Output
• Explanation
• Time complexity
• Solution

# Problem

https://atcoder.jp/contests/atc001/tasks/dfs_a

# Input

$H W$
$c_{0,0} c_{0,1} ... c_{0,W-1}$
$c_{1,0} c_{1,1} ... c_{1,W-1}$
...
c_{H-1,0} c_{H-1,1} ... c_

• $H$ - the length of height of rectangle
• $W$ - the length of base of rectangle
• $c_{i, j}$ - Either of '.', '#', 's', 'g'

# Output

Weather you can get to g from s by going though only ..
You can go up, down, left or up (4 directions).

# Explanation

It can be solved with DFS starting from s.

# Time complexity

$O(H W)$

# Solution

// C++ 14
#include <iostream>
#include <string>
#include <vector>
#include <list>
#include <algorithm>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <unordered_map>
#include <math.h>

#define ll long long
#define Int int
#define loop(x, start, end) for(Int x = start; x < end; x++)
#define loopdown(x, start, end) for(int x = start; x > end; x--)
#define rep(n) for(int x = 0; x < n; x++)
#define span(a,x,y) a.begin()+x,a.begin()+y
#define span_all(a) a.begin(),a.end()
#define len(x) (x.size())
#define last(x) (*(x.end()-1))

using namespace std;

#define MAX_N 501

Int H, W;
vector<bool> C(MAX_N*MAX_N, true);
Int sx, sy, gx, gy;

void dump(Int x, Int y, Int depth) {
  cout << "\033c";
  sleep_for(16ms);
  loop(h,0,H) {
    loop(w,0,W) {
      if (w == x && h == y) cout << "O";
      else cout << ".";
    }
    cout << endl;
  }
}

void input() {
  char x;
  cin >> H >> W;
  loop(h,0,H) {
    loop(w,0,W) {
      cin >> x;
      if (x == '#') C[h*W + w] = false;
      else if (x == 's') sx = w, sy = h;
      else if (x == 'g') gx = w, gy = h;
    }
  }
}

bool dfs(Int x, Int y, Int depth) {
  // dump(x, y, depth);
  if (gx == x && gy == y) return true;
  C[y*W+x] = false;
  loop(dy,-1,2) {
    loop(dx,-1,2) {
      if (dy != 0 && dx != 0) continue;
      Int x_ = x + dx, y_ = y + dy;
      if (x_ < 0 || W <= x_ || y_ < 0 || H <= y_) continue;
      if (!C[y_*W + x_]) continue;
      if (dfs(x_, y_, depth+1)) return true;
    }
  }
  return false;
}

void solve() {
  if (dfs(sx, sy, 0)) cout << "Yes" << endl;
  else cout << "No" << endl;
}

int main(void) {
  input();
  solve();
  return 0;
}