题目

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.

              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.

利用递归解答

/**
 * 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;
        }
        if(root.left==null&&root.right==null&&sum-root.val==0){  //注意要同时有根节点到叶节点的路径，只有根节点是不符合要求的
            return true;
        }
        boolean bl=false;
        boolean br=false;
        if(root.left!=null){
            bl=hasPathSum(root.left,sum-root.val);
        }
        if(root.right!=null){
            br=hasPathSum(root.right,sum-root.val);
        }
        return bl||br;
    }
}

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