代码随想录算法训练营第五十二天 | 图论part03

#include <vector>
#include <iostream>using namespace std;int dir[4][2] = {0, 1, 0, -1, -1, 0, 1, 0};
void dfs(const vector<vector<int>> &grid, vector<vector<bool>> &visited, int x, int y, int& result) {for (int i = 0; i < 4; ++i) {int nextx = x + dir[i][1];int nexty = y + dir[i][0];if (nextx < 0 || nextx >= grid.size()|| nexty < 0 || nexty >= grid[0].size())  continue;if (!visited[nextx][nexty] && grid[nextx][nexty] == 1) {visited[nextx][nexty] = true;result++;dfs(grid, visited, nextx, nexty, result);}}
}int main() {int n, m, result = 0;cin >> n >> m;vector<vector<int>> grid(n, vector<int>(m, 0));for (int i = 0; i < n; ++i) {for (int j = 0; j < m; ++j) {cin >> grid[i][j];}}vector<vector<bool>> visited(n, vector<bool>(m, false));for (int j = 0; j < m; ++j) {if (grid[0][j] == 1 && visited[0][j] == false) {visited[0][j] = true;dfs(grid, visited, 0, j, result);}if (grid[n-1][j] == 1 && visited[n-1][j] == false) {visited[n-1][j] = true;dfs(grid, visited, n-1, j, result);}}for (int i = 0; i < n; ++i) {if (grid[i][0] == 1 && visited[i][0] == false) {visited[i][0] = true;dfs(grid, visited, i, 0, result);}if (grid[i][m-1] == 1 && visited[i][m-1] == false) {visited[i][m-1] = true;dfs(grid, visited, i, m-1, result);}}result = 0;for (int i = 0; i < n; ++i) {for (int j = 0; j < m; ++j) {if (grid[i][j] == 1 && visited[i][j] == false) {result++;visited[i][j] = true;dfs(grid, visited, i, j, result);}}}cout << result;
}

#include <vector>
#include <iostream>using namespace std;int dir[4][2] = {0, 1, 0, -1, -1, 0, 1, 0};
void dfs(vector<vector<int>> &grid, vector<vector<bool>> &visited, int x, int y, bool transfer) {for (int i = 0; i < 4; ++i) {int nextx = x + dir[i][1];int nexty = y + dir[i][0];if (nextx < 0 || nextx >= grid.size()|| nexty < 0 || nexty >= grid[0].size())  continue;if (!visited[nextx][nexty] && grid[nextx][nexty] == 1) {visited[nextx][nexty] = true;if (transfer) {grid[nextx][nexty] = 0;}dfs(grid, visited, nextx, nexty, transfer);}}
}int main() {int n, m;cin >> n >> m;vector<vector<int>> grid(n, vector<int>(m, 0));for (int i = 0; i < n; ++i) {for (int j = 0; j < m; ++j) {cin >> grid[i][j];}}vector<vector<bool>> visited(n, vector<bool>(m, false));for (int j = 0; j < m; ++j) {if (grid[0][j] == 1 && visited[0][j] == false) {visited[0][j] = true;dfs(grid, visited, 0, j, false);}if (grid[n-1][j] == 1 && visited[n-1][j] == false) {visited[n-1][j] = true;dfs(grid, visited, n-1, j, false);}}for (int i = 0; i < n; ++i) {if (grid[i][0] == 1 && visited[i][0] == false) {visited[i][0] = true;dfs(grid, visited, i, 0, false);}if (grid[i][m-1] == 1 && visited[i][m-1] == false) {visited[i][m-1] = true;dfs(grid, visited, i, m-1, false);}}for (int i = 0; i < n; ++i) {for (int j = 0; j < m; ++j) {if (grid[i][j] == 1 && visited[i][j] == false) {visited[i][j] = true;grid[i][j] = 0;dfs(grid, visited, i, j, true);}}}for (int i = 0; i < n; ++i) {for (int j = 0; j < m; ++j) {cout << grid[i][j] << " ";}cout << endl;}
}

#include <iostream>
#include <vector>using namespace std;int dir[4][2] = {0, 1, 0, -1, -1, 0, 1, 0};void dfs(const vector<vector<int>> &grid, vector<vector<bool>> &isVisited,int x, int y) {if (isVisited[x][y]) return;isVisited[x][y] = true;for (int i = 0; i < 4; ++i) {int nextx = x + dir[i][0];int nexty = y + dir[i][1];if (nextx < 0 || nextx >= grid.size() || nexty < 0 || nexty >= grid[0].size()) continue;if (grid[nextx][nexty] < grid[x][y])   continue;dfs(grid, isVisited,nextx, nexty);}
}int main() {int n, m;cin >> n >> m;vector<vector<int>> grid(n, vector<int>(m, 0));for (int i = 0; i < n; ++i) {for (int j = 0; j < m; ++j) {cin >> grid[i][j];}}vector<vector<bool>> Visited1(n, vector<bool>(m, false));vector<vector<bool>> Visited2(n, vector<bool>(m, false));for (int j = 0; j < m; ++j) {dfs(grid, Visited1, 0, j);dfs(grid, Visited2, n - 1, j);}for (int i = 0; i < n; ++i) {dfs(grid, Visited1, i, 0);dfs(grid, Visited2, i, m - 1);}for (int i = 0; i < n; ++i) {for (int j = 0; j < m; ++j) {if (Visited1[i][j] && Visited2[i][j])cout << i << " " << j << endl;}}
}

#include <iostream>
#include <vector>
#include <unordered_map>
#include <unordered_set>
using namespace std;int dir[4][2] = {0, 1, 0, -1, -1, 0, 1, 0};
bool isAllGrid = true; 
void dfs(vector<vector<int>> &grid, vector<vector<bool>> &visited,
int &count, int mark, int x, int y) {if (visited[x][y] == true || grid[x][y] == 0) return;visited[x][y] = true;grid[x][y] = mark;count++;for (int i = 0; i < 4; ++i) {int nextx = x + dir[i][0];int nexty = y + dir[i][1];if (nextx < 0 || nextx >= grid.size() || nexty < 0 || nexty >= grid[0].size()) continue;dfs(grid, visited, count, mark, nextx, nexty);}
}void firstScan(vector<vector<int>> &grid, 
unordered_map<int, int> &gridNum, vector<vector<bool>> &visited) {int mark = 2;for (int i = 0; i < grid.size(); ++i) {for (int j = 0; j < grid[0].size(); ++j) {if (grid[i][j] == 0) isAllGrid = false;if (visited[i][j] == false && grid[i][j] == 1) {int count = 0;dfs(grid, visited, count, mark, i, j);gridNum.emplace(mark, count);mark++;}}}
}int secondScan(vector<vector<int>> &grid, unordered_map<int, int> &gridNum) {int result = 0;unordered_set<int> visitedGrid;for (int i = 0; i < grid.size(); ++i) {for (int j = 0; j < grid[0].size(); ++j) {int count = 1;visitedGrid.clear(); //这里没有考虑到if (grid[i][j] == 0) {for (int a = 0; a < 4; ++a) {int nextx = i + dir[a][0];int nexty = j + dir[a][1];if (nextx < 0 || nextx >= grid.size() || nexty < 0 || nexty >= grid[0].size()) continue;if (visitedGrid.count(grid[nextx][nexty])) continue;count += gridNum[grid[nextx][nexty]];visitedGrid.insert(grid[nextx][nexty]);}}result = max(result, count);}}return result;
}int main() {int n, m;cin >> n >> m;vector<vector<int>> grid(n, vector<int>(m, 0));for (int i = 0; i < n; ++i) {for (int j = 0; j < m; ++j) {cin >> grid[i][j];}}unordered_map<int, int> gridNum;vector<vector<bool>> visited(n, vector<bool>(m, false));firstScan(grid, gridNum, visited);if (isAllGrid) {cout << n * m << endl; // 这个情况也没有考虑到return 0; }cout << secondScan(grid, gridNum);return 0;
}