Added number of Islands

Author: ignacio-chiazzo

LeetcodeProblems/Number_of_Islands.js

@@ -0,0 +1,75 @@
+/*
+Number of Islands
+https://leetcode.com/problems/number-of-islands/
+
+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.
+
+Example 1:
+
+Input:
+11110
+11010
+11000
+00000
+
+Output: 1
+Example 2:
+
+Input:
+11000
+11000
+00100
+00011
+
+Output: 3
+*/
+
+/*
+ * @param {character[][]} grid
+ * @return {number}
+ */
+var numIslands = function(grid) {
+  if(grid.length === 0)
+      return 0;
+  
+  var countIslands = 0;
+  const rowsCount = grid.length;
+  const columnsCount = grid[0].length;
+  for(var i = 0; i < rowsCount; i++) {
+    for(var j = 0; j < columnsCount; j++) {
+      if(grid[i][j] == 1) {
+        countIslands++;
+        colorIsland(grid, i, j, rowsCount, columnsCount);
+      }
+    }
+  }
+  
+  return countIslands;
+};
+
+var colorIsland = function(grid, i, j, rowsCount, columnsCount) {
+  if(i < 0 || j < 0 || i >= rowsCount || j >= columnsCount || grid[i][j] == 0)
+      return;
+  
+  grid[i][j] = 0;
+  
+  colorIsland(grid, i - 1, j, rowsCount, columnsCount);
+  colorIsland(grid, i + 1, j, rowsCount, columnsCount);
+  colorIsland(grid, i, j - 1, rowsCount, columnsCount);
+  colorIsland(grid, i, j + 1, rowsCount, columnsCount);
+}
+
+var main = function() {
+  console.log(numIslands([[1]]));
+  console.log(numIslands([]));
+  console.log(numIslands(
+    [
+      ["1","1","1","1","0"],
+      ["1","1","0","1","0"],
+      ["1","1","0","0","0"],
+      ["0","0","0","0","0"]
+    ])
+  );
+}
+
+module.exports.main = main;

README.md

@@ -14,6 +14,7 @@ Solutions of algorithm problems using Javascript
 | [merge k sorted lists ](/LeetcodeProblems/merge_k_sorted_lists.js)                                   | Hard   | https://leetcode.com/problems/merge-k-sorted-lists/ |
 | [Subarray Sum Equals K ](/LeetcodeProblems/Subarray_Sum_Equals_K.js)                                 | Medium | https://leetcode.com/problems/subarray-sum-equals-k/ | 
 | [3Sum ](/LeetcodeProblems/3Sum.js)                                                                   | Medium | https://leetcode.com/problems/3sum/ | 
+| [NumberOfIslands ](/LeetcodeProblems/Number_of_Islands.js)                                           | Medium | https://leetcode.com/problems/number-of-islands/ | 
 | [Swap Nodes in Pairs](/LeetcodeProblems/Swap_Nodes_in_Pairs.js)                                      | Medium | https://leetcode.com/problems/swap-nodes-in-pairs/ | 
 | [Add Two Numbers ](/LeetcodeProblems/Add_Two_Numbers.js)                                             | Medium | https://leetcode.com/problems/add-two-numbers/  |
 | [Clone Graph ](/LeetcodeProblems/Clone_Graph.js)                                                     | Medium | https://leetcode.com/problems/clone-graph/ |