num of island 數島嶼 系列
阿新 • • 發佈:2021-11-22
1254.Number of Closed Islands
Medium
Given a 2Dgrid
consists of0s
(land)and1s
(water). Anislandis a maximal 4-directionally connected group of0s
and aclosed islandis an islandtotally(all left, top, right, bottom) surrounded by1s.
Return the number ofclosed islands.
Example 1:
Input: grid = [[1,1,1,1,1,1,1,0],[1,0,0,0,0,1,1,0],[1,0,1,0,1,1,1,0],[1,0,0,0,0,1,0,1],[1,1,1,1,1,1,1,0]] Output: 2 Explanation: Islands in gray are closed because they are completely surrounded by water (group of 1s).
Example 2:
Input: grid = [[0,0,1,0,0],[0,1,0,1,0],[0,1,1,1,0]] Output: 1
Example 3:
Input: grid = [[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]] Output: 2
Constraints:
1 <= grid.length, grid[0].length <= 100
0 <= grid[i][j] <=1
解法:其中0的部分為island,但是接觸到四個邊界的island不算,只要按照這個規則進行dfs即可
class Solution { public int closedIsland(int[][] grid) { int count = 0; for( int i=0;i<grid.length;i++){ for(int j=0;j<grid[0].length;j++){if(grid[i][j]==0 && dfs(grid,i,j)) { count++; } } } return count; } private boolean dfs(int[][] grid,int i,int j){ if(i<0||j<0||i>=grid.length||j>=grid[0].length) return false; if(grid[i][j]!=0) return true; grid[i][j]=1; return dfs( grid,i-1,j) & dfs(grid,i+1,j) & dfs(grid,i,j-1) & dfs(grid,i,j+1); } }