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Given an m x n
2D binary grid grid
which represents a map of '1'
s (land) and '0'
s (water), return the number of islands.
An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.
Example 1:
Input: grid = [
["1","1","1","1","0"],
["1","1","0","1","0"],
["1","1","0","0","0"],
["0","0","0","0","0"]
]
Output: 1
Example 2:
Input: grid = [
["1","1","0","0","0"],
["1","1","0","0","0"],
["0","0","1","0","0"],
["0","0","0","1","1"]
]
Output: 3
Constraints:
m == grid.length
n == grid[i].length
1 <= m, n <= 300
grid[i][j]
is '0'
or '1'
.def numIslands(self, grid):
def sink(i, j):
if 0 <= i < len(grid) and 0 <= j < len(grid[i]) and grid[i][j] == '1':
grid[i][j] = '0'
map(sink, (i+1, i-1, i, i), (j, j, j+1, j-1))
return 1
return 0
return sum(sink(i, j) for i in range(len(grid)) for j in range(len(grid[i])))
public class Solution {
char[][] g;
public int numIslands(char[][] grid) {
int islands = 0;
g = grid;
for (int i=0; i<g.length; i++)
for (int j=0; j<g[i].length; j++)
islands += sink(i, j);
return islands;
}
int sink(int i, int j) {
if (i < 0 || i == g.length || j < 0 || j == g[i].length || g[i][j] == '0')
return 0;
g[i][j] = '0';
sink(i+1, j); sink(i-1, j); sink(i, j+1); sink(i, j-1);
return 1;
}
}
class Solution {
public:
int numIslands(vector<vector<char>>& grid) {
int m = grid.size(), n = m ? grid[0].size() : 0, islands = 0, offsets[] = {0, 1, 0, -1, 0};
for (int i = 0; i < m; i++) {
for (int j = 0; j < n; j++) {
if (grid[i][j] == '1') {
islands++;
grid[i][j] = '0';
queue<pair<int, int>> todo;
todo.push({i, j});
while (!todo.empty()) {
pair<int, int> p = todo.front();
todo.pop();
for (int k = 0; k < 4; k++) {
int r = p.first + offsets[k], c = p.second + offsets[k + 1];
if (r >= 0 && r < m && c >= 0 && c < n && grid[r][c] == '1') {
grid[r][c] = '0';
todo.push({r, c});
}
}
}
}
}
}
return islands;
}
};
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