leetcode 89: Path Sum

Path SumOct 14 '12

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.

 

 

/**
 * 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) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(root==null) return false;
        return pathRec(root, 0, sum);
    }
    
    private boolean pathRec(TreeNode root, int parentSum, int sum) {
        if(root.left==null && root.right==null) {
            return parentSum + root.val ==sum;
        }
        
        boolean l=false,r=false;
        
        if(root.right==null) {
             l = pathRec(root.left, parentSum+root.val, sum);
             return l;
        }
        
        if(root.left==null) {
            r = pathRec(root.right, parentSum + root.val, sum);
            return r;
        }
        
        l = pathRec(root.left, parentSum+root.val, sum);
        r = pathRec(root.right, parentSum + root.val, sum);
        return l|r;
    } 
}