A. Лиса и две точки

#include <bits/stdc++.h>

using i32 = int;
using ui32 = unsigned int;
using i64 = long long;
using ui64 = unsigned long long;

const ui32 MSIZE = 51;

std::vector<std::pair<ui32, ui32>> g[MSIZE][MSIZE];
char arr[MSIZE][MSIZE];

i32 dx[4]{0, 0, -1, 1};
i32 dy[4]{-1, 1, 0, 0};

i32 color[MSIZE][MSIZE];

bool Dfs(int x, int y, int px = -1, int py = -1) {
  color[x][y] = 1;
  for (const auto& [nx, ny] : g[x][y]) {
    if (nx == px && ny == py) continue;
    if (color[nx][ny] == 1) {
      return true;
    }
    if (color[nx][ny] == 0) {
      if (Dfs(nx, ny, x, y)) {
        return true;
      }
    }
  }
  color[x][y] = 2;
  return false;
}

i32 main() {
  ui32 n, m;
  scanf("%d%d", &n, &m);
  for (ui32 i = 0; i < n; i++) {
    scanf("%s", arr[i]);
  }

  for (ui32 i = 0; i < n; i++) {
    for (ui32 j = 0; j < m; j++) {
      for (i32 k = 0; k < 4; k++) {
        i32 x = i32(i) + dx[k];
        i32 y = i32(j) + dy[k];
        if (x < 0 or y < 0 or x >= i32(n) or y >= i32(m)) continue;
        if (arr[x][y] != arr[i][j]) continue;
        g[i][j].emplace_back(x, y);
      }
    }
  }
  bool cycleExists = false;
  for (ui32 i = 0; i < n; i++) {
    for (ui32 j = 0; j < m; j++) {
      if (color[i][j] == 0) {
        if (Dfs(i, j)) {
          cycleExists = true;
        }
      }
    }
  }
  puts(cycleExists ? "Yes" : "No");
}