day 31: 543-diameter-of-binary-tree

543-diameter-of-binary-tree/driver.cpp

@@ -0,0 +1,17 @@
+#include "soln.hpp"
+
+int main()
+{
+	// input
+	TreeNode n1 = TreeNode(1);
+	TreeNode n3 = TreeNode(3);
+	TreeNode n6 = TreeNode(6);
+	TreeNode n9 = TreeNode(9);
+	TreeNode n2 = TreeNode(2, &n1, &n3);
+	TreeNode n7 = TreeNode(7, &n6, &n9);
+	TreeNode n4 = TreeNode(4, &n2, &n7);
+	int answer = 4;
+	Solution soln;
+	cout << "Found diameter correctly? " << soln.test(&n4, answer) << endl;
+	return 0;
+}

543-diameter-of-binary-tree/soln.cpp

@@ -0,0 +1,25 @@
+#include "soln.hpp"
+
+int Solution::diameterOfBinaryTree(TreeNode *root)
+{
+	int max_dia = 0;
+	height(root, max_dia);
+	return max_dia;
+}
+
+int Solution::height(TreeNode *subroot, int &max_dia)
+{
+	if (!subroot)
+		return 0;
+	int left_child_height = height(subroot->left, max_dia);
+	int right_child_height = height(subroot->right, max_dia);
+	// max_dia for all in this subtree is left_h + right_h, so check global maximum
+	max_dia = max(max_dia, left_child_height + right_child_height);
+	// for height, we add the edge connecting this subtree to max of child heights
+	return 1 + max(left_child_height, right_child_height);
+}
+
+bool Solution::test(TreeNode *root, int answer)
+{
+	return diameterOfBinaryTree(root) == answer;
+}

543-diameter-of-binary-tree/soln.hpp

@@ -0,0 +1,19 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+struct TreeNode
+{
+	int val;
+	TreeNode *left;
+	TreeNode *right;
+	TreeNode() : val(0), left(nullptr), right(nullptr) {}
+	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+	TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+};
+class Solution
+{
+public:
+	int diameterOfBinaryTree(TreeNode *root);
+	int height(TreeNode *subroot, int &max_dia);
+	bool test(TreeNode *root, int answer);
+};