added largestIsland solution

Author: DevDelvo

dataStructures/graphs/largestIsland.js

@@ -0,0 +1,63 @@
+// Given a non-empty 2D array grid of 0's and 1's, an island is a group of 1's (representing land) connected 4-directionally (horizontal or vertical.) You may assume all four edges of the grid are surrounded by water. Count the number of islands in the given 2D array.
+
+// For Example:
+            
+// const matrix = [
+//     [0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0],
+//     [0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0],
+//     [0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0],
+//     [0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0],
+//     [0, 1, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 0],
+//     [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0],
+//     [0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0],
+//     [0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0]
+// ];
+
+// Output:
+// => 6
+
+const test1 = [
+      [0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0],
+      [0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0],
+      [0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0],
+      [0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0],
+      [0, 1, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 0],
+      [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0],
+      [0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0],
+      [0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0]
+  ];
+
+const largestIsland = matrix => {
+  const seen = {};
+  let maxSize = 0;
+  for (let r = 0; r < matrix.length; r++) {
+    for (let c = 0; c < matrix[r].length; c++) {
+      maxSize = Math.max(calculateSizeOfIsland(r, c, matrix, seen), maxSize);
+    }
+  }
+  return maxSize;
+}
+
+const calculateSizeOfIsland = (r, c, matrix, seen) => {
+  if (
+    seen[[r,c]] || // already seen
+    r < 0 || // r is out of bounds
+    r >= matrix.length || // r is out of bounds
+    c < 0 || // c is out of bounds
+    c >= matrix[r].length || // c is out of bounds
+    matrix[r][c] === 0 // not in an island
+  ) {
+    return 0;
+  }
+  seen[[r,c]] = true;
+
+  return (
+    1 +
+    calculateSizeOfIsland(r + 1, c, matrix, seen) +
+    calculateSizeOfIsland(r -1, c, matrix, seen) +
+    calculateSizeOfIsland(r, c + 1, matrix, seen) +
+    calculateSizeOfIsland(r, c - 1, matrix, seen)
+  )
+}
+
+console.log(largestIsland(test1)); // 6s