# # 【LeetCode】306. Additive Number 解题报告（Python）

## # 题目描述：

A valid additive sequence should contain at least three numbers. Except for the first two numbers, each subsequent number in the sequence must be the sum of the preceding two.

Given a string containing only digits '0'-'9', write a function to determine if it's an additive number.

Note: Numbers in the additive sequence cannot have leading zeros, so sequence 1, 2, 03 or 1, 02, 3 is invalid.

Example 1:

``````Input: "112358"
Output: true
Explanation: The digits can form an additive sequence: 1, 1, 2, 3, 5, 8.
1 + 1 = 2, 1 + 2 = 3, 2 + 3 = 5, 3 + 5 = 8
``````

Example 2:

``````Input: "199100199"
Output: true
Explanation: The additive sequence is: 1, 99, 100, 199.
1 + 99 = 100, 99 + 100 = 199
``````

• How would you handle overflow for very large input integers?

## # 解题方法

``````class Solution(object):
"""
:type num: str
:rtype: bool
"""
return self.dfs(num, [])

def dfs(self, num_str, path):
if len(path) >= 3 and  path[-1] != path[-2] + path[-3]:
return False
if not num_str and len(path) >= 3:
return True
for i in range(len(num_str)):
curr = num_str[:i+1]
if (curr[0] == '0' and len(curr) != 1):
continue
if self.dfs(num_str[i+1:], path + [int(curr)]):
return True
return False
``````

## # 日期

2018 年 6 月 12 日 ———— 实验室上午放假2333刷题吧