mini-parser.py

# Time:  O(n)
# Space: O(h)

# 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,[789]]]",
#
# 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.
#
# """
# 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
       """

   def add(self, elem):
       """
       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):
    def deserialize(self, s):
        if not s:
            return NestedInteger()

        if s[0] != '[':
            return NestedInteger(int(s))

        stk = []

        i = 0
        for j in xrange(len(s)):
            if s[j] == '[':
                stk += NestedInteger(),
                i = j+1
            elif s[j] in ',]':
                if s[j-1].isdigit():
                    stk[-1].add(NestedInteger(int(s[i:j])))
                if s[j] == ']' and len(stk) > 1:
                    cur = stk[-1]
                    stk.pop();
                    stk[-1].add(cur)
                i = j+1

        return stk[-1]