栈和队列_leetcode102

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

class Solution(object):
    def levelOrder(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """

        res = []

        if not root :
            return res

        queue = []

        queue.append(root)

        while queue:
            node = queue.pop()

            res.append(node.val)

            if node.left:
                queue.append(node.left)
            if node.right:
                queue.append(node.right)

        return res





class Solution2(object):
    def levelOrder(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """

        res = []

        if not root :
            return res

        queue = []

        level = 0
        pair = (root,level)
        queue.append(pair)

        while queue:
            pair  = queue.pop()

            if len(res) == pair[1]:
                res.append([])
            res[pair[1]].append(pair[0].val)

            if pair[0].right:
                queue.append((pair[0].right,pair[1]+1))
            if pair[0].left:
                queue.append((pair[0].left,pair[1]+1))



        return res



# 队列中新进的节点都是同一层的节点
class Solution3(object):
    def levelOrder(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """

        res = []

        if not root :
            return res

        queue = []
        queue.append(root)

        while queue:
            level = []

            for i in range(len(queue)): # 这段代码写的不好 20100304
                node = queue.pop(0)
                level.append(node.val)

                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)

            res.append(level)
        return res

# 修改版
class Solution32(object):
    def levelOrder(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """

        res = []

        if not root :
            return res

        queue = []
        queue.append(root)

        while queue:

            level = []
            length = len(queue)
            for i in range(length):  # 这样改的就比较清楚了
                node = queue.pop(0)
                level.append(node.val)

                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)

            res.append(level)
        return res

class Solution4(object):
    def levelOrder(self, root):
        """
        :type root: TreeNode
        :rtype: List[List[int]]
        """

        res = []

        self.level(root,0,res)

        return res

    def level(self,node,lev,res):
        if not node:
            return

        if len(res) == lev:
            res.append([])

        res[lev].append(node.val)

        self.level(node.left,lev+1,res)
        self.level(node.right,lev+1,res)

栈和队列_leetcode102

原文：https://www.cnblogs.com/lux-ace/p/10547334.html