刷题-Path Sum 缺python

原创于 2014-12-05 16:07:59 发布 · 291 阅读

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#java #python

本文探讨了如何确定一棵二叉树中是否存在从根节点到叶子节点的路径，使得这条路径上所有节点值之和等于给定的数值。提供了一个递归算法实现，并通过示例验证了其正确性。

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.

java：

/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public boolean hasPathSum(TreeNode root, int sum) {
if (root == null) return false;
int c = sum - root.val;
boolean res_left=false;
boolean res_right=false;
if (root.left == null && root.right == null && c==0) return true;
else{
if (root.left!=null){
res_left = hasPathSum(root.left,c);
}
if (root.right!=null){
res_right = hasPathSum(root.right,c);
}
return res_left||res_right;

}
}

}