Create 687. Longest Univalue Path

Author: haibarawu

687. Longest Univalue Path

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+/*
+// Given a binary tree, find the length of the longest path where each node in the path has the same value. 
+// This path may or may not pass through the root.
+
+// Note: The length of path between two nodes is represented by the number of edges between them.
+
+Example 1:
+Input:
+
+              5
+             / \
+            4   5
+           / \   \
+          1   1   5
+Output:
+2
+
+Example 2:
+Input:
+
+              1
+             / \
+            4   5
+           / \   \
+          4   4   5
+Output:
+2
+*/
+
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+ 
+class Solution {
+    int result;
+    
+    public int longestUnivaluePath(TreeNode root) {
+        result = 0;
+        arrowLength(root);
+        return result;
+    }
+    
+    public int arrowLength(TreeNode node) {
+        if (node == null) {
+            return 0;
+        }
+        
+        int left = arrowLength(node.left);
+        int right = arrowLength(node.right);
+        
+        int arrowLeft = 0, arrowRight = 0;
+        
+        if (node.left != null && node.left.val == node.val) {
+            arrowLeft += left + 1;
+        }
+        
+        if (node.right != null && node.right.val == node.val) {
+            arrowRight += right + 1;
+        }
+        
+        result = Math.max(result, arrowLeft + arrowRight);
+        
+        return Math.max(arrowLeft, arrowRight);
+    }
+}