LeetCode 200. Number of Islands

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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

这是一道图论的题。我这儿采用dfs算法，将一个岛的元素全部标志为2，遍历整个map，遇到2和0就跳过，累计没有跳过的次数。

/** * Created by kyle on 2016/6/1. */public class NumberOfIsland  {    static  void dfs(char[][] map, int i ,int j){        int m = map.length;        int n = map[0].length;        if(map[i][j] == '0'){            return;        }        if(map[i][j] =='2'){            return;        }        if(map[i][j] == '1'){            map[i][j] = '2';        }        if(i+1 < m){            dfs(map, i+1, j);        }        if(j+1 < n){            dfs(map, i, j+1);        }        if(i-1 >=0){            dfs(map, i-1, j);        }        if( j- 1 >= 0){            dfs(map ,i, j-1);        }    }    static  int numberOfIsland(char[][] grid){        if(grid == null){            return  0;        }        if(grid.length == 0 || grid[0].length == 0){            return  0;        }        int m = grid.length;        int n = grid[0].length;        int count = 0;        for( int i =0 ; i< m ; i++){            for(int j = 0 ; j< n ; j++){                if(grid[i][j] == '1'){                    dfs(grid , i ,j );                  //  show(grid);                    count++;                }            }        }        return  count;    }    static  void show(char[][] islandMap){        System.out.println("island map :");        for(int i =0 ;i< islandMap.length ; i++){            System.out.println(Arrays.toString(islandMap[i]));        }    }    static  public  void main(String[] args){        /*char[][] islandMap = {                {'1','1','1','0','0'},                {'1','1','0','1','0'},                {'0','0','1','0','0'},                {'0','0','0','1','1'},        };*/        char[][] islandMap = {                {'1','1','1'},                {'0','1','0'},                {'1','1','1'}        };       // dfs(islandMap, 0, 0);       // int number = numberOfIsland(new int[0][0]);        int number = numberOfIsland(islandMap);        for(int i =0 ;i< islandMap.length ; i++){            System.out.println(Arrays.toString(islandMap[i]));        }        System.out.println(" number of island : "+ number);    }}

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