LeetCode-- Binary Tree Maximum Path Sum

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int MaxPathSum(TreeNode root) {
    	var max = int.MinValue;
	    CountMax(root, ref max);
	
    	return max;
    }


private int? CountMax(TreeNode root, ref int max)
{
	if(root == null){
		return null;
	}
	
	var leftMax = CountMax(root.left, ref max);
	var rightMax = CountMax(root.right, ref max);
	
	var maxRoute = root.val;
	max = Math.Max(maxRoute, max);
	if(leftMax.HasValue){
		maxRoute = Math.Max(maxRoute, root.val + leftMax.Value);// Max(current , left)
		max = Math.Max(Math.Max(max, leftMax.Value), maxRoute);// Max(left, current , left + current)
	}
	if(rightMax.HasValue){
		maxRoute = Math.Max(maxRoute, root.val + rightMax.Value);// Max(currnet, left, right)
		max = Math.Max(Math.Max(max, rightMax.Value), maxRoute);// Max(left, right, current , right + current)
	}
	if(leftMax.HasValue && rightMax.HasValue){
		max = Math.Max(root.val + leftMax.Value + rightMax.Value, max);//Max(left ,right, current ,  right + current, left+right +current)
	}
	
	return maxRoute;
}


}

LeetCode-- Binary Tree Maximum Path Sum

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原文地址：http://blog.csdn.net/lan_liang/article/details/50144507