No of Islands done

Author: rampatra

src/main/java/com/leetcode/arrays/NumberOfIslands.java

@@ -0,0 +1,107 @@
+package com.leetcode.arrays;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * Level: Medium
+ * Link: https://leetcode.com/problems/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.
+ * <p>
+ * Example 1:
+ * Input:
+ * 11110
+ * 11010
+ * 11000
+ * 00000
+ * Output: 1
+ * <p>
+ * Example 2:
+ * Input:
+ * 11000
+ * 11000
+ * 00100
+ * 00011
+ * Output: 3
+ *
+ * @author rampatra
+ * @since 2019-08-07
+ */
+public class NumberOfIslands {
+
+    /**
+     * The idea is simple and straightforward. Once we encounter land ('1' in grid) we drown the island or change the
+     * neighboring '1's to '0's. Therefore, the number of '1's we encounter, we can say that we have that many islands.
+     * <p>
+     * Time Complexity: O(n)
+     * Space Complexity: O(n)
+     * Runtime: <a href="https://leetcode.com/submissions/detail/249754904/">1 ms</a>.
+     *
+     * @param grid
+     * @return
+     */
+    public static int numIslands(char[][] grid) {
+        int count = 0;
+
+        for (int i = 0; i < grid.length; i++) {
+            for (int j = 0; j < grid[0].length; j++) {
+                if (grid[i][j] == '1') {
+                    drownTheIsland(grid, i, j);
+                    count++;
+                }
+            }
+        }
+
+        return count;
+    }
+
+    private static void drownTheIsland(char[][] grid, int i, int j) {
+        if (i < 0 || j < 0 || i >= grid.length || j >= grid[0].length || grid[i][j] == '0') {
+            return;
+        }
+
+        grid[i][j] = '0';
+
+        drownTheIsland(grid, i, j + 1);
+        drownTheIsland(grid, i, j - 1);
+        drownTheIsland(grid, i + 1, j);
+        drownTheIsland(grid, i - 1, j);
+    }
+
+    public static void main(String[] args) {
+        assertEquals(1, numIslands(new char[][]{
+                {'1', '1', '1', '1', '0'},
+                {'1', '1', '0', '1', '0'},
+                {'1', '1', '0', '0', '0'},
+                {'0', '0', '0', '0', '0'}
+        }));
+
+        assertEquals(2, numIslands(new char[][]{
+                {'1', '1', '1', '1', '0'},
+                {'1', '1', '0', '1', '0'},
+                {'1', '1', '0', '0', '0'},
+                {'0', '0', '0', '1', '0'}
+        }));
+
+        assertEquals(1, numIslands(new char[][]{
+                {'1', '1', '1', '1', '1'},
+                {'1', '1', '1', '1', '1'},
+                {'1', '1', '1', '1', '1'},
+                {'1', '1', '1', '1', '1'}
+        }));
+
+        assertEquals(1, numIslands(new char[][]{
+                {'1'}
+        }));
+
+        assertEquals(0, numIslands(new char[][]{
+                {'0'}
+        }));
+
+        assertEquals(0, numIslands(new char[][]{
+                {}
+        }));
+    }
+}

src/main/java/com/leetcode/arrays/ValidTriangleNumber.java

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+package com.leetcode.arrays;
+
+import java.util.Arrays;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * Level: Medium
+ * Problem Link: https://leetcode.com/problems/valid-triangle-number/
+ * Problem Description:
+ * Given an array consists of non-negative integers, your task is to count the number of triplets chosen from the array
+ * that can make triangles if we take them as side lengths of a triangle.
+ * <p>
+ * Example 1:
+ * Input: [2,2,3,4]
+ * Output: 3
+ * Explanation:
+ * Valid combinations are:
+ * 2,3,4 (using the first 2)
+ * 2,3,4 (using the second 2)
+ * 2,2,3
+ * <p>
+ * Note:
+ * The length of the given array won't exceed 1000.
+ * The integers in the given array are in the range of [0, 1000].
+ *
+ * @author rampatra
+ * @since 2019-08-07
+ */
+public class ValidTriangleNumber {
+
+    public static int triangleNumber(int[] nums) {
+        int l = 0;
+        int r = nums.length - 1;
+        int noOfTriangles = 0;
+
+        Arrays.sort(nums);
+
+        // todo
+
+        return noOfTriangles;
+    }
+
+    public static void main(String[] args) {
+        assertEquals(3, triangleNumber(new int[]{2, 2, 3, 4}));
+    }
+}