# Leetcode: Mini Parser

Mini Parser

Similar Problems:

Given a nested list of integers represented as a string, implement a parser to deserialize it.

Each element is either an integer, or a list — whose elements may also be integers or other lists.

Note: You may assume that the string is well-formed:

• String is non-empty.
• String does not contain white spaces.
• String contains only digits 0-9, [, – ,, ].
```Example 1:

Given s = "324",

You should return a NestedInteger object which contains a single integer 324.
```
```Example 2:

Given s = "[123,[456,]]",

Return a NestedInteger object containing a nested list with 2 elements:

1. An integer containing value 123.
2. A nested list containing two elements:
i.  An integer containing value 456.
ii. A nested list with one element:
a. An integer containing value 789.
```

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

```## Blog link: https://code.dennyzhang.com/mini-parser
# """
# This is the interface that allows for creating nested lists.
# You should not implement it, or speculate about its implementation
# """
#class NestedInteger(object):
#    def __init__(self, value=None):
#        """
#        If value is not specified, initializes an empty list.
#        Otherwise initializes a single integer equal to value.
#        """
#
#    def isInteger(self):
#        """
#        @return True if this NestedInteger holds a single integer, rather than a nested list.
#        :rtype bool
#        """
#
#        """
#        Set this NestedInteger to hold a nested list and adds a nested integer elem to it.
#        :rtype void
#        """
#
#    def setInteger(self, value):
#        """
#        Set this NestedInteger to hold a single integer equal to value.
#        :rtype void
#        """
#
#    def getInteger(self):
#        """
#        @return the single integer that this NestedInteger holds, if it holds a single integer
#        Return None if this NestedInteger holds a nested list
#        :rtype int
#        """
#
#    def getList(self):
#        """
#        @return the nested list that this NestedInteger holds, if it holds a nested list
#        Return None if this NestedInteger holds a single integer
#        :rtype List[NestedInteger]
#        """
class Solution(object):
## Basic Ideas: Stack
##     Whenever we found '[', DO NOT push.
##         We initialize a empty NestedInteger as place holder
##     Whenever we found ']', we combine the last 2 place holers
##     Whenever we found digits/'-', look ahead to get what we need.
##               Then construct NestedInteger, then combine it into last place holder
##
## Complexity: Time O(n), Space O(n)
def deserialize(self, s):
"""
:type s: str
:rtype: NestedInteger
"""
if len(s) == 0: return None
if s.find('[') == -1: return NestedInteger(int(s))

stack = []
for word in s.split(','):
i = 0
while i< len(word):
if word[i] == '[':
stack.append(NestedInteger())
i += 1
elif word[i] == ']':
n1 = stack.pop()
n2 = stack.pop()
stack.append(n2+n1)
i += 1
else:
# keep looking ahead until we get an non-digits
string = ''
while i<len(word) and (word[i].isdigit() or word[i] == '-'):
string = "%s%s" % (string, word[i])
i += 1
n = stack.pop()
stack.append(n + NestedInteger(int(string)))
return stack

## Basic Ideas: Stack
##              Whenever we found '[', push
##              Whenever we found ']', we keep poping until we find a '['
##
## Complexity: Time O(n), Space O(n)
def deserialize(self, s):
"""
:type s: str
:rtype: NestedInteger
"""
if len(s) == 0: return None
if s.find('[') == -1: return NestedInteger(int(s))

stack = []
for word in s.split(','):
num_str = ''
for ch in word:
if ch == '[':
stack.append(ch)
continue
if ch != ']':
num_str = '%s%s' % (num_str, ch)
else:
if num_str != '':
stack.append(NestedInteger(int(num_str)))
num_str = ''
# The sequence we get is right from left, but we need left from right.
l = []
while True:
element = stack.pop()
if element == '[':
break
l.insert(0, element)
n = NestedInteger() 