[leetcode]Number of Islands-优快云博客

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Number of Islands

Given a 2d grid map of '1's (land) and '0's (water), count 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:

Answer: 1

Example 2:

Answer: 3

解题思路：递归遍历将所有相连的‘1’置回0

public class Solution {
    public int numIslands(char[][] grid) {
        int islandsCnt = 0;
        
        if(grid == null) return 0;
    	
        for(int i = 0; i < grid.length; i++){
        	for(int j = 0; j < grid[i].length; j++){
        		if(grid[i][j] != '0'){
        			innerNumIslands(grid, i, j);
        			islandsCnt++;
        		}
        	}
        }
        
    	return islandsCnt;        
    }

    public void innerNumIslands(char[][] grid, int r, int c){
    	if(grid == null) return;
    	
    	int rows = grid.length;
    	int columns = grid[0].length;
    	
    	if(r >= rows || r < 0) return;
    	if(c >= columns || c < 0) return;
    	if(grid[r][c] == '0') return;
    	
    	if(grid[r][c] != '0') grid[r][c] = '0';
    	//向左
    	innerNumIslands(grid, r, c - 1);
    	//向右
    	innerNumIslands(grid, r, c + 1);
    	//向上
    	innerNumIslands(grid, r - 1, c);
    	//向下
    	innerNumIslands(grid, r + 1, c);
    }
}