Mini Parser

Desicription

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:

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Given s = "324",

You should return a NestedInteger object which contains a single integer 324.

Example 2:

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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.

Solution

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/**
* // This is the interface that allows for creating nested lists.
* // You should not implement it, or speculate about its implementation
* class NestedInteger {
* public:
* // Constructor initializes an empty nested list.
* NestedInteger();
*
* // Constructor initializes a single integer.
* NestedInteger(int value);
*
* // Return true if this NestedInteger holds a single integer, rather than a nested list.
* bool isInteger() const;
*
* // Return the single integer that this NestedInteger holds, if it holds a single integer
* // The result is undefined if this NestedInteger holds a nested list
* int getInteger() const;
*
* // Set this NestedInteger to hold a single integer.
* void setInteger(int value);
*
* // Set this NestedInteger to hold a nested list and adds a nested integer to it.
* void add(const NestedInteger &ni);
*
* // Return the nested list that this NestedInteger holds, if it holds a nested list
* // The result is undefined if this NestedInteger holds a single integer
* const vector<NestedInteger> &getList() const;
* };
*/
class Solution {
public:
NestedInteger deserialize(const std::string& s) {
auto stack = std::stack<NestedInteger>{};
int number = 0;
bool flag = true;
bool haveNumber = false;
for(const auto& c : s) {
switch(c) {
case '[':
stack.push(NestedInteger{});
break;
case ']':
if(flag == false) {
number = -number;
}
if(haveNumber == true) {
stack.top().add(NestedInteger{number});
number = 0;
flag = true;
haveNumber = false;
}

if(stack.size() == 1) {
return stack.top();
} else {
auto tmpNestedInteger = stack.top();
stack.pop();
stack.top().add(tmpNestedInteger);
}
break;
case ',':
if(flag == false) {
number = -number;
}
if(haveNumber == true) {
stack.top().add(NestedInteger{number});
number = 0;
flag = true;
haveNumber = false;
}
break;
case '-':
flag = false;
break;
default:
number = number * 10 + c - '0';
haveNumber = true;
break;
}
}
if(number != 0) {
if(flag == false) {
number = -number;
}
if(haveNumber == true) {
stack.push(NestedInteger{number});
}
}
return stack.empty() ? NestedInteger{0} : stack.top();
}
};