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| 1 | +/* |
| 2 | + * @lc app=leetcode id=200 lang=java |
| 3 | + * |
| 4 | + * [200] Number of Islands |
| 5 | + * |
| 6 | + * https://leetcode.com/problems/number-of-islands/description/ |
| 7 | + * |
| 8 | + * algorithms |
| 9 | + * Medium (48.72%) |
| 10 | + * Total Accepted: 956.8K |
| 11 | + * Total Submissions: 2M |
| 12 | + * Testcase Example: '[["1","1","1","1","0"],["1","1","0","1","0"],["1","1","0","0","0"],["0","0","0","0","0"]]' |
| 13 | + * |
| 14 | + * Given an m x n 2d grid map of '1's (land) and '0's (water), return the |
| 15 | + * number of islands. |
| 16 | + * |
| 17 | + * An island is surrounded by water and is formed by connecting adjacent lands |
| 18 | + * horizontally or vertically. You may assume all four edges of the grid are |
| 19 | + * all surrounded by water. |
| 20 | + * |
| 21 | + * |
| 22 | + * Example 1: |
| 23 | + * |
| 24 | + * |
| 25 | + * Input: grid = [ |
| 26 | + * ["1","1","1","1","0"], |
| 27 | + * ["1","1","0","1","0"], |
| 28 | + * ["1","1","0","0","0"], |
| 29 | + * ["0","0","0","0","0"] |
| 30 | + * ] |
| 31 | + * Output: 1 |
| 32 | + * |
| 33 | + * |
| 34 | + * Example 2: |
| 35 | + * |
| 36 | + * |
| 37 | + * Input: grid = [ |
| 38 | + * ["1","1","0","0","0"], |
| 39 | + * ["1","1","0","0","0"], |
| 40 | + * ["0","0","1","0","0"], |
| 41 | + * ["0","0","0","1","1"] |
| 42 | + * ] |
| 43 | + * Output: 3 |
| 44 | + * |
| 45 | + * |
| 46 | + * |
| 47 | + * Constraints: |
| 48 | + * |
| 49 | + * |
| 50 | + * m == grid.length |
| 51 | + * n == grid[i].length |
| 52 | + * 1 <= m, n <= 300 |
| 53 | + * grid[i][j] is '0' or '1'. |
| 54 | + * |
| 55 | + * |
| 56 | + */ |
| 57 | + |
| 58 | + |
| 59 | +// public class Solution { |
| 60 | +// |
| 61 | +// private int n; |
| 62 | +// private int m; |
| 63 | +// |
| 64 | +// public int numIslands(char[][] grid) { |
| 65 | +// int count = 0; |
| 66 | +// n = grid.length; |
| 67 | +// if (n == 0) return 0; |
| 68 | +// m = grid[0].length; |
| 69 | +// for (int i = 0; i < n; i++){ |
| 70 | +// for (int j = 0; j < m; j++) { |
| 71 | +// if (grid[i][j] == '1') { |
| 72 | +// DFSMarking(grid, i, j); |
| 73 | +// ++count; |
| 74 | +// } |
| 75 | +// } |
| 76 | +// } |
| 77 | +// return count; |
| 78 | +// } |
| 79 | +// |
| 80 | +// private void DFSMarking(char[][] grid, int i, int j) { |
| 81 | +// if (i < 0 || j < 0 || i >= n || j >= m || grid[i][j] != '1') return; |
| 82 | +// grid[i][j] = '0'; |
| 83 | +// DFSMarking(grid, i + 1, j); |
| 84 | +// DFSMarking(grid, i - 1, j); |
| 85 | +// DFSMarking(grid, i, j + 1); |
| 86 | +// DFSMarking(grid, i, j - 1); |
| 87 | +// } |
| 88 | +// } |
| 89 | + |
| 90 | +class Solution { |
| 91 | + |
| 92 | + private int W; |
| 93 | + private int H; |
| 94 | + |
| 95 | + public int numIslands(char[][] grid) { |
| 96 | + |
| 97 | + W = grid.length; |
| 98 | + H = grid[0].length; |
| 99 | + |
| 100 | + if (W == 0) return 0; |
| 101 | + |
| 102 | + int islands = 0; |
| 103 | + for (int i = 0; i < W; ++i) { |
| 104 | + for (int j = 0; j < H; ++j) { |
| 105 | + if (grid[i][j] == '1') { |
| 106 | + dfs(grid, i, j); |
| 107 | + ++islands; |
| 108 | + } |
| 109 | + } |
| 110 | + } |
| 111 | + return islands; |
| 112 | + } |
| 113 | + |
| 114 | + public void dfs(char[][] grid, int x, int y) { |
| 115 | + if (isOutOfBounds(grid, x, y) || grid[x][y] != '1') return; |
| 116 | + grid[x][y] = '0'; |
| 117 | + dfs(grid, x, y + 1); // top |
| 118 | + dfs(grid, x + 1, y); // right |
| 119 | + dfs(grid, x, y - 1); // down |
| 120 | + dfs(grid, x - 1, y); // left |
| 121 | + } |
| 122 | + |
| 123 | + public boolean isOutOfBounds(char[][] grid, int x, int y) { |
| 124 | + if (x < 0 || y < 0 || x >= W || y >= H) |
| 125 | + return true; |
| 126 | + |
| 127 | + return false; |
| 128 | + } |
| 129 | +} |
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