【LeetCode OJ】Path Sum II

Problem Link:

http://oj.leetcode.com/problems/path-sum-ii/

The basic idea here is same to that of Path Sum. However, since the problem is asking for all possible root-to-leaf paths, so we should use BFS but not DFS.

The python code is as follows.

# Definition for a  binary tree node
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    # @param root, a tree node
    # @param sum, an integer
    # @return a boolean
    def pathSum(self, root, sum):
        """
        BFS from the root to leaves.
        For each leaf, check the path sum with the target sum
        """
        if not root:
            return []
        q = [([root],0)]
        res = []
        while q:
            new_q = []
            for path, s in q:
                n = path[-1]
                s += n.val
                # If path is a root-to-leaf path
                if n.left == n.right == None:
                    if sum == s:
                        res.append([p.val for p in path])
                else:  # Continue BFS
                    if n.left:
                        new_q.append((path+[n.left], s))
                    if n.right:
                        new_q.append((path+[n.right],s))
            q = new_q
        return res