112. Path Sum

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

For example:
Given the below binary tree and sum = 22,

              5
             / \
            4   8
           /   / \
          11  13  4
         /  \      \
        7    2      1

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

 

 

  public bool HasPathSum(TreeNode root, int sum) {
         if(root == null) return false;
         return Judge(root,sum);
        
    }
    
    private bool Judge(TreeNode root, int sum)
    {
        if(root == null) return sum==0;
        if(root.left == null && root.right == null) return sum == root.val;
        return HasPathSum(root.left,sum- root.val)||HasPathSum(root.right,sum - root.val);
    }

此题可能还有一个延伸为找到符合的路径。可参考113题。 http://www.cnblogs.com/renyualbert/p/5863271.html