画图 （FloodFill Algorithm）全网首发！

#include <iostream>
#include <vector>

using namespace std;
int n, m, q, x, y, x1, yy1, x2, y2, op;
char c;

void print(vector<vector<char>>& mat) {
  for (int y = 0; y < m; ++y) {
    for (int x = 0; x < n; ++x) printf("%c", mat[y][x]);
    printf("\n");
  }
}

// depth first search
void dfs(vector<vector<char>>& grid,
         vector<vector<int>>& visited, 
         int x, int y, char c) {

  if (x < 0 || y < 0 || x == n || y == m 
      || grid[y][x] == '-' || grid[y][x] == '|' || grid[y][x] == '+'
      || visited[y][x])
    return;

  grid[y][x] = c; // fill
  visited[y][x] = 1; // mark as visited

  dfs(grid, visited, x - 1, y, c);
  dfs(grid, visited, x + 1, y, c);
  dfs(grid, visited, x, y - 1, c);
  dfs(grid, visited, x, y + 1, c);
}

int main(void) {
  scanf("%d %d %d", &n, &m, &q);
  vector<vector<char>> grid(m, vector<char>(n, '.'));

  while (q--) {
    cin >> op;
    if (op == 0) {
      cin >> x1 >> yy1 >> x2 >> y2;

      if (x1 > x2) swap(x1, x2);
      if (yy1 > y2) swap(yy1, y2);

      if (x1 == x2) { // 画竖线
        for (int y = m - 1 - yy1; y >= m - 1 - y2; --y)
          grid[y][x1] = grid[y][x1] == '-' || grid[y][x1] == '+'  ? '+' : '|';
      } else { // 画横线
        for (int x = x1; x <= x2; ++x)
          grid[m - 1 - yy1][x] = grid[m - 1 - yy1][x] == '|' || grid[m - 1 - yy1][x] == '+'  ? '+' : '-';
      }
    } else {
      cin >> x >> y >> c;
      vector<vector<int>> visited(m, vector<int>(n));
      dfs(grid, visited, x, m - 1 - y, c);
    }
  }

  print(grid);
  return 0;
}