// 1254. Number of Closed Islands #include "leetcode.h" /* * given 2d 'grid' consists of 0's (land) and 1's (water). an island is a * maximal four directionally connected group of 0's and a closed island is an * island totally (all left, top, right, bottom) surrouned by 1's. return the * number of closed islands. */ class Solution { int dx[4] = {0, 0, -1, 1}, dy[4] = {1, -1, 0, 0}; bool is_valid(vvd(int) & grid, int i, int j, int r, int c) { if (i >= 0 && i < r && j >= 0 && j < c && grid[i][j] == 0) return true; else return false; } void dfs(vvd(int) & grid, int i, int j, int r, int c) { grid[i][j] = 1; for (int x = 0; x < 4; ++x) { int new_x = i + dx[x]; int new_y = i + dy[x]; if (is_valid(grid, new_x, new_y, r, c)) dfs(grid, new_x, new_y, r, c); } } public: int closedIsland(vvd(int) & grid) { int r = grid.size(), c = grid[0].size(), ans = 0; for (int i = 0; i < r; ++i) for (int j = 0; j < c; ++j) if (i * j == 0 || i == r - 1 || j == c - 1) if (grid[i][j] == 0) dfs(grid, i, j, r, c); for (int i = 0; i < r; ++i) for (int j = 0; j < c; ++j) if (grid[i][j] == 0) { ans++; dfs(grid, i, j, r, c); } return ans; } }; int main() { Solution obj; vvd(int) g1 = {{1, 1, 1, 1, 1, 1, 1, 0}, {1, 0, 0, 0, 0, 1, 1, 0}, {1, 0, 0, 0, 0, 1, 0, 1}, {1, 1, 1, 1, 1, 1, 1, 0}}; vvd(int) g2 = {{0, 0, 1, 0, 0}, {0, 1, 0, 1, 0}}; vvd(int) g3 = {{1, 1, 1, 1, 1, 1, 1}, {1, 0, 0, 0, 0, 0, 1}, {1, 0, 1, 1, 1, 0, 1}, {1, 0, 1, 0, 1, 0, 1}, {1, 0, 1, 1, 1, 0, 1}, {1, 0, 0, 0, 0, 0, 1}, {1, 1, 1, 1, 1, 1, 1}}; printf("%d\n", obj.closedIsland(g1)); // expect: 2 printf("%d\n", obj.closedIsland(g2)); // expect: 1 printf("%d\n", obj.closedIsland(g3)); // expect: 2 }