959. Regions Cut By Slashes

In a N x N grid composed of 1 x 1 squares, each 1 x 1 square consists of a /, , or blank space. These characters divide the square into contiguous regions.

(Note that backslash characters are escaped, so a is represented as "\".)

Return the number of regions.

Example 1:
Input:
[
  " /",
  "/ "
]
Output: 2
Explanation: The 2x2 grid is as follows:

Example 2:
Input:
[
  " /",
  "  "
]
Output: 1
Explanation: The 2x2 grid is as follows:

Example 3:
Input:
[
  "\\/",
  "/\\"
]
Output: 4
Explanation: (Recall that because \ characters are escaped, "\\/" refers to \/, and "/\\" refers to /\.)
The 2x2 grid is as follows:

Example 4:
Input:
[
  "/\\",
  "\\/"
]
Output: 5
Explanation: (Recall that because \ characters are escaped, "/\\" refers to /\, and "\\/" refers to \/.)
The 2x2 grid is as follows:

Example 5:
Input:
[
  "//",
  "/ "
]
Output: 3

Explanation: The 2x2 grid is as follows:
Note:
1 <= grid.length == grid[0].length <= 30 gridi is either '/', '', or ' '.

难度：medium

题目：
给定一个由1X1的方块组成的网格，每个方块由/ '' ‘ ’（空字符） 3 个元素组成，这些元素将大方块分成若干小的连续区域。求连续区域的个数。

思路：
将每个小方格用3 Ｘ 3的0、1数组表示。因此题目就转成了0、1矩阵中求0的连续区域个数。

/ 转换成
001
010
100
'\' 转换成
100
010
001
‘ ’ 转换成
000
000
000

Runtime: 12 ms, faster than 85.37% of Java online submissions for Regions Cut By Slashes.

class Solution {
    /**
    *      001
    * / -> 010
    *      100
    *
    *      100
    * \ -> 010
    *      001
    *
    *      000
    * ' '->000
    *      000
    *
    * convert to find the isolated 0s by 1
    */
    public int regionsBySlashes(String[] grid) {
        int row = grid.length;
        int trippleRow = 3 * row;
        int[][] iGrid = new int[trippleRow][trippleRow];
        
        for (int i = 0; i < trippleRow; i += 3) {
            char[] sc = grid[i / 3].toCharArray();
            for (int j = 0; j < trippleRow; j += 3) {
                char c = sc[j / 3];
                if ('/' == c) {
                    iGrid[i][j + 2] = iGrid[i + 1][j + 1] = iGrid[i + 2][j] = 1;
                } else if ('\\' == c) {
                    iGrid[i][j] = iGrid[i + 1][j + 1] = iGrid[i + 2][j + 2] = 1; 
                } 
            }
        }
        
        int count = 0;
        for (int i = 0; i < trippleRow; i++) {
            for (int j = 0; j < trippleRow; j++) {
                if (0 == iGrid[i][j]) {
                    colorGrid(iGrid, i, j);
                    count++;
                }
            }
        }
                           
        return count;
    }

    private void colorGrid(int[][] grid, int i, int j) {
        grid[i][j] = 1;
        // up
        if (0 == grid[Math.max(i - 1, 0)][j]) {
            colorGrid(grid, i - 1, j);
        }

        // down
        if (0 == grid[Math.min(i + 1, grid.length - 1)][j]) { 
            colorGrid(grid, i + 1, j);
        }
        // left
        if (0 == grid[i][Math.max(j - 1, 0)]) { 
            colorGrid(grid, i, j - 1);
        }
        // right
        if (0 == grid[i][Math.min(j + 1, grid[0].length - 1)] ) { 
            colorGrid(grid, i, j + 1);
        }
    }
}