Number of Islands

Description:

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

Code:

 1 #define MAX 500
 2 
 3 struct vertex
 4 {
 5     int row;
 6     int col;
 7     vertex(int x, int y):row(x),col(y){
 8     }
 9 };
10 
11 class Solution {
12 private:
13 bool visit[MAX][MAX];
14 public:
15 
16     void BFSTraverse(vector<vector<char>>& grid, int i, int j)
17     {
18         visit[i][j] = true;
19         deque<vertex>m;
20         m.push_back(vertex(i,j));
21         while (!m.empty())
22         {
23             vertex v = m.front();
24             m.pop_front();
25             int mRow = v.row;
26             int mCol = v.col;
27             for (int k = 1; k <= 4; ++k)
28             {
29                 switch (k)
30                 {
31                     case 1:
32                         mRow = v.row-1;
33                         mCol = v.col;
34                         break;
35                     case 2:
36                         mRow = v.row+1;
37                         mCol = v.col;
38                         break;
39                     case 3:
40                         mRow = v.row;
41                         mCol = v.col-1;
42                         break;
43                     case 4:
44                         mRow = v.row;
45                         mCol = v.col+1;
46                         break;
47                 }
48                 if ( mRow >= 0 && mRow < grid.size() && mCol >=0 && mCol < grid[0].size() 
49                 && grid[mRow][mCol] == '1' && visit[mRow][mCol] == false)
50                 {
51                     visit[mRow][mCol] = true;
52                     m.push_back( vertex(mRow,mCol) );
53                 }
54             }
55         }
56     }
57     
58     int numIslands(vector<vector<char>>& grid) {
59         size_t row = grid.size();
60         if (row == 0)
61             return 0;
62         size_t col = grid[0].size();
63          //注意二维数组的初始化不可以直接用visit[MAX][MAX] = {false}，应采用for循环（memset函数似乎也可以）
64         for (int i = 0; i < row; ++i)
65         {
66             for (int j = 0; j < col; ++j)
67                 visit[i][j] = false;
68         }
69         int result = 0;
70         for (int i = 0; i < row; ++i)
71         {
72             for (int j = 0; j < col; ++j)
73             {
74                 if ( grid[i][j]=='1' && visit[i][j] == false )
75                 {
76                     ++result;
77                     BFSTraverse(grid, i, j);
78                 }
79             }
80         }
81         return result;
82     }
83 };

View Code