543. Diameter of Binary Tree (#70)

Author: Kohei Asai

solutions/diameterOfBinaryTree.test.ts

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+import { createBinaryTreeNode } from "../utilities/TreeNode";
+import diameterOfBinaryTree from "./diameterOfBinaryTree";
+
+describe("543. Diameter of Binary Tree", () => {
+  test("#1", () => {
+    expect(diameterOfBinaryTree(createBinaryTreeNode([1, 2, 3, 4, 5]))).toBe(3);
+  });
+
+  test("#2", () => {
+    expect(diameterOfBinaryTree(createBinaryTreeNode([1]))).toBe(0);
+  });
+
+  test("#3", () => {
+    expect(diameterOfBinaryTree(null)).toBe(0);
+  });
+
+  test("#4", () => {
+    expect(
+      diameterOfBinaryTree(
+        createBinaryTreeNode([
+          4,
+          -7,
+          -3,
+          null,
+          null,
+          -9,
+          -3,
+          9,
+          -7,
+          -4,
+          null,
+          6,
+          null,
+          -6,
+          -6,
+          null,
+          null,
+          0,
+          6,
+          5,
+          null,
+          9,
+          null,
+          null,
+          -1,
+          -4,
+          null,
+          null,
+          null,
+          -2
+        ])
+      )
+    ).toBe(8);
+  });
+});

solutions/diameterOfBinaryTree.ts

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+import { TreeNode } from "../utilities/TreeNode";
+
+// 543. Diameter of Binary Tree
+// https://leetcode.com/problems/diameter-of-binary-tree/
+export default function diameterOfBinaryTree<T>(
+  node: TreeNode<T> | null
+): number {
+  function getHeightAndDiameter(node: TreeNode<T> | null): [number, number] {
+    if (node === null) return [-1, -1];
+
+    const [leftHeight, leftDiameter] = getHeightAndDiameter(node.left);
+    const [rightHeight, rightDiameter] = getHeightAndDiameter(node.right);
+
+    return [
+      Math.max(leftHeight, rightHeight) + 1,
+      Math.max(leftHeight + rightHeight + 2, leftDiameter, rightDiameter)
+    ];
+  }
+
+  if (!node) return 0;
+
+  return getHeightAndDiameter(node)[1];
+}