Leetcode刷题记录-20181020

给定一个二叉树，求其最小深度

如果没有根节点，返回0；如果有根节点，判断左右孩子，有左孩子，返回左孩子最小深度+1；有右孩子，返回右孩子最小深度+1；左右孩子都有，返回左右孩子最小深度+1；都没有，返回1

 1 class Solution:
 2     def minDepth(self, root):
 3         """
 4         :type root: TreeNode
 5         :rtype: int
 6         """
 7         if not root:
 8             return 0
 9         a = root.right
10         b = root.left
11         if a and b:
12             return min(self.minDepth(a),self.minDepth(b))+1
13         if a and not b:
14             return self.minDepth(a)+1
15         if not a and b:
16             return self.minDepth(b)+1
17         if not a and not b:
18             return 1

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112.Path Sum

寻找二叉树中是否存在一条节点和为给定数值的路径，路径为从根节点到叶子

 1 class Solution:
 2     def hasPathSum(self, root, sum):
 3         """
 4         :type root: TreeNode
 5         :type sum: int
 6         :rtype: bool
 7         """
 8         result = sum
 9         if root:
10             p = root.left
11             q = root.right
12             if not p and not q:
13                 if result == root.val:
14                     return True
15                 else:
16                     return False
17             if not p:
18                 return self.hasPathSum(q,result-root.val)
19             if not q:
20                 return self.hasPathSum(p,result-root.val)
21             if p and q:
22                 return self.hasPathSum(p,result-root.val) or self.hasPathSum(q,result-root.val)
23         else:
24             return False

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118.Pascal's Triangle

杨辉三角形

每层数字列表 = 对（[0，上一层数字，0]）列表内数据依次相加得到

 1 class Solution:
 2     def generate(self,numRows):
 3         """
 4         :type numRows: int
 5         :rtype: List[List[int]]
 6         """
 7         result = []
 8         if numRows == 0:
 9             return []
10         if numRows >=1:
11             result.append([1]) 
12         
13         
14         for i in range(1,numRows):
15             if i == 0:
16                 result.append([1])
17             temp = result[-1]
18             temp = [0] + temp
19             temp.append(0)
20             each_level = []
21             for j in range(len(temp)-1):
22                 each_level.append(temp[j]+temp[j+1])
23             result.append(each_level)
24         return result

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Leetcode刷题记录-20181020

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