update 200.number-of-islands.java

Author: marklcrns

200.number-of-islands.java

@@ -0,0 +1,129 @@
+/*
+ * @lc app=leetcode id=200 lang=java
+ *
+ * [200] Number of Islands
+ *
+ * https://leetcode.com/problems/number-of-islands/description/
+ *
+ * algorithms
+ * Medium (48.72%)
+ * Total Accepted:    956.8K
+ * Total Submissions: 2M
+ * Testcase Example:  '[["1","1","1","1","0"],["1","1","0","1","0"],["1","1","0","0","0"],["0","0","0","0","0"]]'
+ *
+ * Given an m x n 2d grid map of '1's (land) and '0's (water), return 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:
+ *
+ *
+ * Input: grid = [
+ * ⁠ ["1","1","1","1","0"],
+ * ⁠ ["1","1","0","1","0"],
+ * ⁠ ["1","1","0","0","0"],
+ * ⁠ ["0","0","0","0","0"]
+ * ]
+ * Output: 1
+ *
+ *
+ * Example 2:
+ *
+ *
+ * Input: grid = [
+ * ⁠ ["1","1","0","0","0"],
+ * ⁠ ["1","1","0","0","0"],
+ * ⁠ ["0","0","1","0","0"],
+ * ⁠ ["0","0","0","1","1"]
+ * ]
+ * Output: 3
+ *
+ *
+ *
+ * Constraints:
+ *
+ *
+ * m == grid.length
+ * n == grid[i].length
+ * 1 <= m, n <= 300
+ * grid[i][j] is '0' or '1'.
+ *
+ *
+ */
+
+
+// public class Solution {
+//
+// 	private int n;
+// 	private int m;
+//
+// 	public int numIslands(char[][] grid) {
+// 		int count = 0;
+// 		n = grid.length;
+// 		if (n == 0) return 0;
+// 		m = grid[0].length;
+// 		for (int i = 0; i < n; i++){
+// 			for (int j = 0; j < m; j++) {
+// 				if (grid[i][j] == '1') {
+// 					DFSMarking(grid, i, j);
+// 					++count;
+// 				}
+// 			}
+// 		}
+// 		return count;
+// 	}
+//
+// 	private void DFSMarking(char[][] grid, int i, int j) {
+// 		if (i < 0 || j < 0 || i >= n || j >= m || grid[i][j] != '1') return;
+// 		grid[i][j] = '0';
+// 		DFSMarking(grid, i + 1, j);
+// 		DFSMarking(grid, i - 1, j);
+// 		DFSMarking(grid, i, j + 1);
+// 		DFSMarking(grid, i, j - 1);
+// 	}
+// }
+
+class Solution {
+
+	private int W;
+	private int H;
+
+	public int numIslands(char[][] grid) {
+
+		W = grid.length;
+		H = grid[0].length;
+
+		if (W == 0) return 0;
+
+		int islands = 0;
+		for (int i = 0; i < W; ++i) {
+			for (int j = 0; j < H; ++j) {
+				if (grid[i][j] == '1') {
+					dfs(grid, i, j);
+					++islands;
+				}
+			}
+		}
+		return islands;
+	}
+
+	public void dfs(char[][] grid, int x, int y) {
+		if (isOutOfBounds(grid, x, y) || grid[x][y] != '1') return;
+		grid[x][y] = '0';
+		dfs(grid, x, y + 1); // top
+		dfs(grid, x + 1, y); // right
+		dfs(grid, x, y - 1); // down
+		dfs(grid, x - 1, y); // left
+	}
+
+	public boolean isOutOfBounds(char[][] grid, int x, int y) {
+		if (x < 0 || y < 0 || x >= W || y >= H)
+			return true;
+
+		return false;
+	}
+}