grid47 Exploring patterns and algorithms
Sep 29, 2024
6 min read
Solution to LeetCode 385: Mini Parser Problem
Given a string s representing a serialized nested list, implement a parser to deserialize it and return the deserialized NestedInteger.
Problem
Approach
Steps
Complexity
Input: The input is a string s representing the serialized nested list.
Example: s = '[789, [1011, 1213], 1415]'
Constraints:
• 1 <= s.length <= 50,000
• s consists of digits, square brackets '[]', negative sign '-', and commas ','
• The string s is the serialization of a valid NestedInteger
• All values are within the range [-10^6, 10^6]
Output: The output is a NestedInteger object representing the deserialized nested list.
Example: Output: [789, [1011, 1213], 1415]
Constraints:
• The deserialized object should match the nested list structure.
Goal: The goal is to parse the serialized string and reconstruct the correct NestedInteger object.
Steps:
• Traverse the string character by character.
• Identify numbers and handle their potential negative signs.
• Identify opening brackets '[' and create new NestedInteger objects for lists.
• Identify closing brackets ']' and complete the current list.
• Use a stack to maintain the current state while parsing nested lists.
Goal: The solution must be efficient to handle large inputs.
Steps:
• The solution should handle up to 50,000 characters in the input string efficiently.
Assumptions:
• The input string is a valid serialized NestedInteger and will not contain malformed lists.
• Input: Input: '[789, [1011, 1213], 1415]'
• Explanation: The string represents a list with three elements: 789, a nested list [1011, 1213], and 1415.
Approach: The approach involves parsing the string to correctly build a NestedInteger object, using a stack to handle nested lists and ensuring that each element is correctly identified as an integer or list.
Observations:
• We need to distinguish between integers and lists while parsing the string.
• A stack will be useful to manage the nesting of lists during parsing.
Steps:
• Initialize an empty stack.
• Iterate through each character of the string.
• When encountering a number, extract the number and add it as a NestedInteger.
• When encountering a '[' symbol, push a new NestedInteger (representing a new list) onto the stack.
• When encountering a ']' symbol, pop the top of the stack and add it to the NestedInteger object beneath it.
Empty Inputs:
• Ensure that input strings are non-empty and valid.
Large Inputs:
• Handle input strings as large as 50,000 characters efficiently.
Special Values:
• Ensure the solution handles negative numbers and deep nesting correctly.
Constraints:
• The solution must parse the string in linear time relative to its length.
NestedInteger deserialize(string s) {
function<bool(char)> isnumber = [](char c) { return (c =='-') || isdigit(c); };
stack<NestedInteger> stk;
stk.push(NestedInteger());
for(auto it = s.begin(); it != s.end();) {
constchar&c =*it;
if(isnumber(c)) {
auto it2 = find_if_not(it, s.end(), isnumber);
int val = stoi(string(it, it2));
stk.top().add(NestedInteger(val));
it = it2;
}
else {
if(c =='[') {
stk.push(NestedInteger());
} elseif (c ==']') {
NestedInteger ni = stk.top();
stk.pop();
stk.top().add(ni);
}
it++;
}
}
NestedInteger res = stk.top().getList().front();
return res;
}
1 : Function Definition
NestedInteger deserialize(string s) {
This is the function definition of 'deserialize' which takes a string 's' as input and returns a NestedInteger object.
