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June 14, 2020 16:49
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/* | |
In a 2d matrix, there are islands are surrounded by water. | |
For easier understand, we use 1 stands for islands, 0 stands for water. | |
A example would be: | |
1 0 0 0 | |
1 1 1 0 | |
0 0 1 0 | |
1 0 0 0 | |
There are 2 islands in the matrix. | |
the first one is: | |
1 | |
1 1 1 | |
1 | |
The second one is | |
1 (on the index of( 3, 0) | |
Find numbers of islands by giving a 2d matrix. | |
*/ | |
class Island { | |
public static void main(String[] args) { | |
int[][] matrix = {{1, 0, 0, 0}, | |
{1, 1, 1, 0}, | |
{0, 0, 1, 0}, | |
{1, 0, 0, 0}}; | |
System.out.println(numOfIslands(matrix)); | |
// here should print 2 | |
int[][] matrix2 = {{1, 0, 0, 0}, | |
{1, 0, 1, 0}, | |
{0, 0, 1, 0}, | |
{1, 0, 0, 0}}; | |
System.out.println(numOfIslands(matrix2)); | |
// here should print 3 | |
} | |
private int numOfIslands(int[][] matrix) { | |
int countIslands = 0; | |
for(int i = 0; i < matrix.length; i++) { | |
for(int j = 0; j < matrix[0].length; j++) { | |
if(matrix[i][j] == 1) { | |
DFS(matrix, i, j); | |
countIslands++; | |
} | |
} | |
} | |
return countIslands; | |
} | |
private void DFS(int[][] matrix, int row, int col) { | |
if(row < 0 || row >= matrix.length || col < 0 || col > matrix[0].length || matrix[row][col] != 1) { | |
return; | |
} | |
matrix[row][col] = 2; | |
DFS(matrix, row+1, col); | |
DFS(matrix, row-1, col); | |
DFS(matrix, row, col+1); | |
DFS(matrix, row, col-1); | |
} | |
} | |
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