Max Path Sum Tree Solution

java/124-Binary-Tree-Maximum-Path-Sum.java

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+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+class Solution {
+
+    int[] res = new int[1];
+
+    public int maxPathSum(TreeNode root) {
+        res[0] = root.val;
+        dfs(root);
+        return res[0];
+    }
+
+    private int dfs(TreeNode node) {
+        if (node == null) return 0;
+
+        int leftMax = dfs(node.left);
+        int rightMax = dfs(node.right);
+
+        leftMax = Math.max(leftMax, 0);
+        rightMax = Math.max(rightMax, 0);
+
+        int allMax = leftMax + rightMax + node.val;
+        res[0] = Math.max(res[0], allMax);
+
+
+        return node.val + Math.max(leftMax, rightMax);
+    }
+}