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/**

* 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 must contain at least one node and does not need to go through the root.

*

* For example:

* Given the below binary tree,

*

* 1

* / \

* 2 3

*

* Return 6.

*/

public class BinaryTreeMaximumPathSum124 {

private int maxSum;

public int maxPathSum(TreeNode root) {

maxSum = Integer.MIN_VALUE;

maxBranch(root);

return maxSum;

}

private int maxBranch(TreeNode root) {

if (root == null) return 0;

int valueLeft = Math.max(0, maxBranch(root.left));

int valueRight = Math.max(0, maxBranch(root.right));

maxSum = Math.max(maxSum, root.val + valueLeft + valueRight);

return Math.max(valueLeft, valueRight) + root.val;

}

public static void main(String[] args) {

BinaryTreeMaximumPathSum124 btmps = new BinaryTreeMaximumPathSum124();

TreeNode root1 = new TreeNode(2);

root1.left = new TreeNode(1);

root1.right = new TreeNode(3);

TreeNode root2 = new TreeNode(-3);

System.out.println(btmps.maxPathSum(root1));

System.out.println(btmps.maxPathSum(root2));

}

}