Leetcode-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.

 

Solution:

/**
 * 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;
            
        boolean res = hasPathSumRecur(root,sum);
        return res;
    }
    
    public boolean hasPathSumRecur(TreeNode curNode, int residual){
        if (curNode.left==null&&curNode.right==null){
            if (residual==curNode.val)
               return true;
            else 
               return false;
        }
        
        boolean left = false;
        boolean right = false;
        
        if (curNode.left!=null)
            left = hasPathSumRecur(curNode.left,residual-curNode.val);
            
        if (curNode.right!=null)
            right = hasPathSumRecur(curNode.right,residual-curNode.val);
        
        if (left||right)
           return true;
        else
           return false;
    }
}

This is a recursive problem. No hard.

转载于:https://www.cnblogs.com/lishiblog/p/4083040.html