Merge pull request neetcode-gh#113 from ArwaNayef/patch-9

Create 543-Diameter-of-Binary-Tree

Author: neetcode-gh

Diff for: java/543-Diameter-of-Binary-Tree.java

@@ -0,0 +1,32 @@
+class Solution {
+      private static int treeDiameter = 0;
+
+    public int diameterOfBinaryTree(TreeNode root) {
+   calculateHeight(root);
+    return treeDiameter-1;
+  }
+
+  private static int calculateHeight(TreeNode currentNode) {
+    if (currentNode == null)
+      return 0;
+
+    int leftTreeHeight = calculateHeight(currentNode.left);
+    int rightTreeHeight = calculateHeight(currentNode.right);
+
+    // if the current node doesn't have a left or right subtree, we can't have
+    // a path passing through it, since we need a leaf node on each side
+    if (leftTreeHeight != 0 && rightTreeHeight != 0) {
+
+      // diameter at the current node will be equal to the height of left subtree +
+      // the height of right sub-trees + '1' for the current node
+      int diameter = leftTreeHeight + rightTreeHeight + 1;
+
+      // update the global tree diameter
+      treeDiameter = Math.max(treeDiameter, diameter);
+    }
+
+    // height of the current node will be equal to the maximum of the heights of
+    // left or right subtrees plus '1' for the current node
+    return Math.max(leftTreeHeight, rightTreeHeight) + 1;
+  }
+}