[LeetCode] 385. Mini Parser

[LeetCode] 385. Mini Parser

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.

Thought process:
Iterate through the string. There are five cases:

1. Digit: keep track of current number.
2. [: push the current NestedInteger onto stack and create a new NestedInteger.
3. -: set sign to -1.
4. ,: if the previous character is a digit, add the number into current NestedInteger. If the previous character is ], add the current NestedInteger to previous NestedInteger.
5. ]: current NestedInteger is finished. Pop the NestedInteger from top of the stack.

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