1. Title
Binary Tree Maximum Path Sum
2. Http address
https://leetcode.com/problems/binary-tree-maximum-path-sum/
3. The question
Given a binary tree, find the maximum path sum.
For this problem, a path is defined as any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The path does not need to go through the root.
For example:
Given the below binary tree,
1
/
2 3
Return 6.
4. My code(AC)
1 //DFS res[0] = sub tree max; res[1] = from root max; 2 public static int [] maxPathSumTwoHelp(TreeNode root){ 3 4 int res [] = new int[2]; 5 int res_left[]; 6 int res_right[]; 7 8 if( root.left != null && root.right != null) 9 { 10 res_left = maxPathSumTwoHelp(root.left); 11 res_right = maxPathSumTwoHelp(root.right); 12 13 res[1] = Math.max(res_left[1], res_right[1]) + root.val; 14 res[1] = Math.max(res[1], root.val); 15 res[0] = Math.max(res_left[0], res_right[0]); 16 res[0] = Math.max(res[0], res_left[1] + res_right[1] + root.val); 17 res[0] = Math.max(res[0], res[1]); 18 19 }else{ 20 if( root.left != null && root.right == null) 21 { 22 res_left = maxPathSumTwoHelp(root.left); 23 res[1] = Math.max(res_left[1] + root.val, root.val); 24 res[0] = Math.max(res_left[0], root.val); 25 res[0] = Math.max(res[0], res[1]); 26 }else if( root.right != null && root.left == null) 27 { 28 res_right = maxPathSumTwoHelp(root.right); 29 res[1] = Math.max(res_right[1] + root.val, root.val); 30 res[0] = Math.max(res_right[0], root.val); 31 res[0] = Math.max(res[0], res[1]); 32 }else{ 33 res[0] = root.val; 34 res[1] = root.val; 35 } 36 } 37 return res; 38 } 39 // Accepted 40 public static int maxPathSumTwo(TreeNode root){ 41 if( root == null) 42 return 0; 43 int res[] = maxPathSumTwoHelp(root); 44 return res[0]; 45 }