Refactor code structure for improved readability and maintainability

Author: theroyakash

.python-version

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+3.13

docs/cp31/1000.md

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+# 1000 Rated problems
+
+1. [Binary String Transformation Problem](#binary-string-transformation-problem)
+
+
+## Binary String Transformation Problem
+Problem link on [codeforces](https://codeforces.com/problemset/problem/1913/B)
+
+### Problem Statement
+
+Given a binary string `s`, transform it into a "good" string `t` where every position differs from the original string (`t[i] ≠ s[i]`).
+
+**Available operations:**
+
+- **Delete** a character (cost: 1 coin)
+- **Swap** any two characters (cost: 0 coins)
+
+**Goal:** Find the minimum cost to create a good string.
+
+### Solution Approach
+
+#### Key Insight
+
+Since swaps are free, we can rearrange characters at no cost. The optimal strategy is to:
+
+1. **Swap characters** to maximize positions where `t[i] ≠ s[i]`
+2. **Delete excess characters** that cannot be repositioned
+
+#### Algorithm Logic
+
+The solution uses a **greedy matching approach**:
+
+```
+For each position i in the original string:
+  - If s[i] = '1', try to place a '0' at position i
+  - If s[i] = '0', try to place a '1' at position i
+  - Track remaining available 0s and 1s
+```
+
+#### Special Cases
+
+1. **Single character** → Must delete it (cost: 1)
+2. **Equal 0s and 1s** → Perfect swap exists (cost: 0)
+3. **Only 0s or only 1s** → Must delete all (cost: n)
+
+#### Core Implementation
+
+```cpp
+int zeros = count('0');
+int ones = count('1');
+
+// Greedy assignment
+for each character c in s:
+    if c == '1':
+        use a '0' → zeros--
+    else:
+        use a '1' → ones--
+    
+    if ran out of needed characters:
+        remaining positions must be deleted
+        break
+```
+
+#### Code
+```cpp
+void solve() {
+    string s; cin >> s;
+    if (s.size() == 1) {
+        std::cout << 1 << "\n"; return;
+    }
+
+    int zeros = 0;
+    int ones = 0;
+    for (auto c : s) {
+        if (c == '0') {
+            zeros++;
+        } else {
+            ones++;
+        }
+    }
+
+    if (zeros == ones) {
+        std::cout << 0 << "\n"; return;
+    }
+
+    if (zeros == 0 or ones == 0) {
+        std::cout << s.size() << "\n"; return;
+    }
+
+    int t = 0;
+    for (int i = 0; i < s.size(); i++) {
+        char c = s[i];
+        if (c == '1') {
+            t++; zeros--;
+            if (zeros < 0) {
+                t--;
+                std::cout << s.size() - t << "\n"; return;
+            }
+        } else if (c == '0') {
+            t++; ones--;
+            if (ones < 0) {
+                t--;
+                std::cout << s.size() - t << "\n"; return;
+            }
+        }
+    }
+}
+```
+
+#### Complexity
+
+- **Time:** O(n) - only pass twice through the string
+- **Space:** O(1) - only counters needed
+
+### Example Walkthrough
+
+**Input:** `s = "1100"`
+
+- Initial: zeros = 2, ones = 2
+- Position 0: `s[0] = '1'` → use `'0'` (zeros = 1) ✓
+- Position 1: `s[1] = '1'` → use `'0'` (zeros = 0) ✓
+- Position 2: `s[2] = '0'` → use `'1'` (ones = 1) ✓
+- Position 3: `s[3] = '0'` → use `'1'` (ones = 0) ✓
+
+**Result:** `t = "0011"`, cost = **0** (perfect swap)
+
+
+
+**Input:** `s = "111000"`
+
+- Initial: zeros = 3, ones = 3
+- Positions 0-2: consume all 3 zeros
+- Positions 3-5: consume all 3 ones
+
+**Result:** cost = **0**
+
+
+
+**Input:** `s = "11100"`
+
+- Initial: zeros = 2, ones = 3
+- Position 0-1: use 2 zeros (zeros = 0)
+- Position 2: need zero but none left → **stop**
+- Successfully placed: 2 characters
+- Must delete: 5 - 2 = **3 characters**
+
+**Result:** cost = **3**

docs/cp31/cp31.md

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+# CP 31 sheet
+This sheet is curated by Priyansh31dec. Can be found [here](https://www.tle-eliminators.com/cp-sheet). This part of the website contains solutions I submitted for the problems in the popular CP31 sheet.
+
+CP 31 sheet is divided into ratings $\in (800, 900, 1000, 1100, \dots 1900)$. For each rating we have a total of 31 tasks to solve. I recommend starting from $800$ rated problems itself.
+
+## Rated Problems
+- [1000 rated problems](./1000.md)

docs/index.md

@@ -45,7 +45,7 @@ This material categorizes coding interview problems into a set of **12 patterns*
 9. [Heaps overview](https://algorithms.theroyakash.com/heaps/heap-pq/) and [heap problems](https://algorithms.theroyakash.com/heaps/problems/) and [2 heaps problems](https://algorithms.theroyakash.com/2heaps/problems/).
 10. [Greedy algorithms](https://algorithms.theroyakash.com/greedy/problems/)
 11. [Dynamic Programming](https://algorithms.theroyakash.com/dp/problems/)
-12.  Bit Manipulation (With C/C++) (coming soon)
+12. [CP 31 Sheet](/cp31/cp31)
 
 ## Problem Counter
 The following table is meant to represent the amount of problems has a full analysis in the website. Maybe incorrectly represented upto 1-2 problems.

docs/io.md

@@ -1,11 +1,28 @@
 # :pencil: Standard input output usage
 
-## Taking data in and writing data out to a file
-In some of the problems in SDE 1 and SDE 2 online coding rounds, you have to take care of the program inputs.
+## Taking fast input output
+In some of the problems in SDE 1 and SDE 2 online coding rounds, you have to take care of the program inputs. Use this following two lines of code to increase your i/o speed in competitive programming contests.
+
+Brief explanation:
+
+- If you include `ios::sync_with_stdio(false)`, then mixing C (`scanf`, `printf`) and C++ (`cin`, `cout`) style I/O may produce unexpected results. The upside is that both `cin / cout` become faster.
+- Including `cin.tie(nullptr)` will reduce the runtime if you are interleaving `cin` and `cout` (as is the case in the task at hand).
+
+```cpp
+int main() {
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
 
+    /* code */
+
+    return 0;
+}
+```
+
+## Taking data in and writing data out to a file
 Here is an example of how we can write all inputs to a text file and then run our algorithms.
 
-You must add 2 files called "input.txt" and "output.txt" in the same directory add the function in the code, then in the `main()` function just call the function `fileIO()` to have the input taken from input.txt and the output written to output.txt.
+You must add 2 files called `input.txt` and `output.txt` in the same directory add the function in the code, then in the `main()` function just call the function `fileIO()` to have the input taken from `input.txt` and the output written to output.txt.
 
 ```cpp
 void fileIO() {
@@ -23,7 +40,7 @@ int main() {
 ```
 
 ### Input
-Now in the input.txt file, you design as the inputs are given in the following case the input was
+Now in the `input.txt` file, you design as the inputs are given in the following case the input was
 
 ```
 3