add binary tree maximum path sum

Author: Tessa1217

binary-tree-maximum-path-sum/Tessa1217.java

@@ -0,0 +1,42 @@
+/**
+ * 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 {
+
+    // 최대 Path 누적 합
+    int maxPathSumVal = Integer.MIN_VALUE;
+
+    // 시간복잡도: O(n), 공간복잡도: O(h) h as height of tree
+    public int maxPathSum(TreeNode root) {
+        maxPathSumChecker(root);
+        return maxPathSumVal;    
+    }
+
+    // 재귀
+    private int maxPathSumChecker(TreeNode node) {
+
+        if (node == null) {
+            return 0;
+        }
+
+        int leftMax = Math.max(maxPathSumChecker(node.left), 0);
+        int rightMax = Math.max(maxPathSumChecker(node.right), 0);
+
+        maxPathSumVal = Math.max(node.val + leftMax + rightMax, maxPathSumVal);
+
+        return node.val + Math.max(leftMax, rightMax);
+    }
+}
+