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dsa-solutions/lc-solutions/0300-0399/0385-Mini-Parser.md

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+---
+id: mini-parser
+title: Mini Parser
+sidebar_label: 0385 - Mini Parser
+tags:
+  - String
+  - Stack
+  - Depth First Search
+description: "This is a solution to the Mini Parser problem on LeetCode."
+---
+
+## Problem Description
+
+Given a string s represents the serialization of a nested list, implement a parser to deserialize it and return the deserialized `NestedInteger`.
+
+Each element is either an integer or a list whose elements may also be integers or other lists.
+
+### Examples
+
+**Example 1:**
+
+```
+Input: s = "324"
+Output: 324
+Explanation: You should return a NestedInteger object which contains a single integer 324.
+
+```
+**Example 2:**
+```
+
+Input: s = "[123,[456,[789]]]"
+Output: [123,[456,[789]]]
+Explanation: 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
+
+```
+### Constraints
+
+- `1 <= s.length <= 5 * 10^4`
+- `s is the serialization of valid NestedInteger`
+- `All the values in the input are in the range [-10^6, 10^6]`
+
+## Solution for Mini Parser
+
+### Approach 
+
+This solution uses a stack to record the `NestedInteger`'s.
+At the very beginning, an empty NestedInteger is placed in the stack. This NestedInteger will be regarded as a list that holds one but only one NestedInteger, which will be returned in the end.
+`Logic: When encountering '[', the stack has one more element. When encountering ']', the stack has one less element`.
+
+## Code in Different Languages
+
+<Tabs>
+<TabItem value="cpp" label="C++">
+  <SolutionAuthor name="@agarwalhimanshugaya"/>
+
+```cpp
+class Solution {
+public:
+    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();) {
+            const char & 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());
+                }
+                else if (c == ']') {
+                    NestedInteger ni = stk.top();
+                    stk.pop();
+                    stk.top().add(ni);
+                }
+                ++it;
+            }
+        }
+
+        NestedInteger result = stk.top().getList().front();
+        return result;
+    }
+};
+```
+</TabItem>
+<TabItem value="java" label="Java">
+  <SolutionAuthor name="@agarwalhimanshugaya"/>
+
+```java
+public NestedInteger deserialize(String s) {
+    if (s.isEmpty())
+        return null;
+    if (s.charAt(0) != '[') // ERROR: special case
+        return new NestedInteger(Integer.valueOf(s));
+
+    Stack<NestedInteger> stack = new Stack<>();
+    NestedInteger curr = null;
+    int l = 0; // l shall point to the start of a number substring; 
+               // r shall point to the end+1 of a number substring
+    for (int r = 0; r < s.length(); r++) {
+        char ch = s.charAt(r);
+        if (ch == '[') {
+            if (curr != null) {
+                stack.push(curr);
+            }
+            curr = new NestedInteger();
+            l = r+1;
+        } else if (ch == ']') {
+            String num = s.substring(l, r);
+            if (!num.isEmpty())
+                curr.add(new NestedInteger(Integer.valueOf(num)));
+            if (!stack.isEmpty()) {
+                NestedInteger pop = stack.pop();
+                pop.add(curr);
+                curr = pop;
+            }
+            l = r+1;
+        } else if (ch == ',') {
+            if (s.charAt(r-1) != ']') {
+                String num = s.substring(l, r);
+                curr.add(new NestedInteger(Integer.valueOf(num)));
+            }
+            l = r+1;
+        }
+    }
+
+    return curr;
+}
+```
+
+</TabItem>
+<TabItem value="python" label="Python">
+  <SolutionAuthor name="@agarwalhimanshugaya"/>
+
+```python
+class Solution:
+    def deserialize(self, s):
+        stack, num, last = [], "", None
+        for c in s:
+            if c.isdigit() or c == "-": num += c
+            elif c == "," and num:
+                stack[-1].add(NestedInteger(int(num)))
+                num = ""
+            elif c == "[":
+                elem = NestedInteger()
+                if stack: stack[-1].add(elem)
+                stack.append(elem)
+            elif c == "]":
+                if num:
+                    stack[-1].add(NestedInteger(int(num)))
+                    num = ""
+                last = stack.pop()
+        return last if last else NestedInteger(int(num))
+```
+</TabItem>
+</Tabs>
+
+## Complexity Analysis
+
+### Time Complexity: $O(N)$
+
+### Space Complexity: $O(N)$
+
+## References
+
+- **LeetCode Problem**: [Kth Largest Element in a Stream](https://leetcode.com/problems/mini-parser/description/)
+
+- **Solution Link**: [Kth Largest Element in a Stream](https://leetcode.com/problems/mini-parser/solutions/)