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MaximumPathSumBinaryTree.java
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MaximumPathSumBinaryTree.java
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package Leetcode;
/**
* @author kalpak
*
* A path in a binary tree is a sequence of nodes where each pair of adjacent nodes in the sequence has an edge connecting them.
* A node can only appear in the sequence at most once. Note that the path does not need to pass through the root.
*
* The path sum of a path is the sum of the node's values in the path.
*
* Given the root of a binary tree, return the maximum path sum of any path.
*
* Example 1:
* Input: root = [1,2,3]
* Output: 6
* Explanation: The optimal path is 2 -> 1 -> 3 with a path sum of 2 + 1 + 3 = 6.
*
*
* Example 2:
* Input: root = [-10,9,20,null,null,15,7]
* Output: 42
* Explanation: The optimal path is 15 -> 20 -> 7 with a path sum of 15 + 20 + 7 = 42.
*
* Constraints:
*
* The number of nodes in the tree is in the range [1, 3 * 104].
* -1000 <= Node.val <= 1000
*/
public class MaximumPathSumBinaryTree {
static int result = Integer.MIN_VALUE;
public static int maxPathSum(TreeNode root) {
dfsMaxPathSum(root);
return result;
}
private static int dfsMaxPathSum(TreeNode root) {
// Base Case
if(root == null)
return 0;
// Induction step: Get the left and right max path sum to compute the current max path sum
int leftMaxSum = Math.max(0, dfsMaxPathSum(root.left));
int rightMaxSum = Math.max(0, dfsMaxPathSum(root.right));
// update the result - max path sum for this node
result = Math.max(result, root.val + leftMaxSum + rightMaxSum);
// return back the best path, which is maximum
return root.val + Math.max(leftMaxSum, rightMaxSum);
}
public static void main(String[] args) {
TreeNode root = new TreeNode(-10);
root.left = new TreeNode(9);
root.right = new TreeNode(20);
root.right.left = new TreeNode(15);
root.right.right = new TreeNode(7);
System.out.println(maxPathSum(root));
}
}