[leetcode]695. Max Area of Island小岛最大面积

佚名 6年前 (2019-05-16) 随笔 1432人围观抢沙发百度已收录

Given a non-empty 2D array grid of 0's and 1's, an island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are surrounded by water.

Find the maximum area of an island in the given 2D array. (If there is no island, the maximum area is 0.)

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Example 1:

[[0,0,1,0,0,0,0,1,0,0,0,0,0],
 [0,0,0,0,0,0,0,1,1,1,0,0,0],
 [0,1,1,0,1,0,0,0,0,0,0,0,0],
 [0,1,0,0,1,1,0,0,1,0,1,0,0],
 [0,1,0,0,1,1,0,0,1,1,1,0,0],
 [0,0,0,0,0,0,0,0,0,0,1,0,0],
 [0,0,0,0,0,0,0,1,1,1,0,0,0],
 [0,0,0,0,0,0,0,1,1,0,0,0,0]]

Given the above grid, return 6. Note the answer is not 11, because the island must be connected 4-directionally.

Example 2:

[[0,0,0,0,0,0,0,0]]

Given the above grid, return 0.

Note: The length of each dimension in the given grid does not exceed 50.

Solution1： DFS

code

 1 class Solution {
 2    public int maxAreaOfIsland(int[][] grid) {
 3         // corner case 
 4         int max = 0;
 5         if ( grid == null || grid.length==0 || grid[0].length==0) return 0;    
 6         for (int i = 0; i< grid.length;i++) {
 7             for (int j = 0; j<grid[i].length;j++) {
 8                 if (grid[i][j]== 1) {
 9                     int[] count = new int[1];
10                     helper(grid, i, j, count);
11                     max = Math.max(max , count[0]);
12                 }
13             }
14         }
15         return max;
16     }
17     
18     private void helper(int[][] grid, int i, int j, int[] count) {
19         // base case
20         if ((i<0) || (j<0) || (i>=grid.length) || (j>=grid[0].length)
21            || grid[i][j] != 1 ) {            
22             return;
23         }   
24         // recursive rule 
25         count[0]++;
26         grid[i][j] = -1;  // mark visited
27         helper(grid, i+1, j, count);
28         helper(grid, i-1, j, count);
29         helper(grid, i, j+1, count);
30         helper(grid, i, j-1, count);
31     }   
32 }