LeetCode – Mini Parser (Java)

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 and "[],"

For example,

```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.
```

Java Solution

To solve this problem, we should add more example to make clear what is the expected output. For example, s = "[123,[456],789]" is a legal input.

```public NestedInteger deserialize(String s) { Stack<NestedInteger> stack = new Stack<>(); StringBuilder sb = new StringBuilder();   for(int i=0; i<s.length(); i++){ char c = s.charAt(i); switch(c){ case '[': NestedInteger ni = new NestedInteger(); stack.push(ni); break;   case ']': if(sb.length()>0){ //123, not [456], stack.peek().add(new NestedInteger(Integer.parseInt(sb.toString()))); sb=sb.delete(0, sb.length()); }   NestedInteger top = stack.pop(); if(stack.isEmpty()){ return top; }else{ stack.peek().add(top); }   break; case ',': if(sb.length()>0){ //hande case "123," not "[456]," stack.peek().add(new NestedInteger(Integer.parseInt(sb.toString()))); sb=sb.delete(0, sb.length()); }   break;   default: //digits sb.append(c); } }   //handle case "123" if(sb.length()>0){ return new NestedInteger(Integer.parseInt(sb.toString())); }   return null; }```
Category >> Algorithms
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