vault backup: 2022-07-12 09:08:19

OJ notes/pages/Leetcode Reverse-String.md

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+# Leetcode Reverse String
+
+#### 2022-07-12 08:50
+
+> ##### Algorithms:
+> #algorithm #recursion 
+> ##### Data structures:
+> #DS #array 
+> ##### Difficulty:
+> #coding_problem #difficulty-easy
+> ##### Additional tags:
+> #leetcode
+> ##### Revisions:
+> N/A
+
+##### Related topics:
+```expander
+tag:#recursion
+```
+ 
+- [[Leetcode Insert-Into-a-Binary-Search-Tree]]
+- [[Leetcode Invert-Binary-Tree]]
+- [[Leetcode Pascal's-Triangle]]
+- [[Leetcode Path-Sum]]
+- [[Leetcode Reverse-Linked-List]]
+- [[Leetcode Symmetric-Tree]]
+ 
+
+##### Links:
+- [Link to problem](https://leetcode.com/problems/reverse-string/)
+___
+### Problem
+
+Write a function that reverses a string. The input string is given as an array of characters `s`.
+
+You must do this by modifying the input array [in-place](https://en.wikipedia.org/wiki/In-place_algorithm) with `O(1)` extra memory.
+
+#### Examples
+
+**Example 1:**
+
+**Input:** s = ["h","e","l","l","o"]
+**Output:** ["o","l","l","e","h"]
+
+**Example 2:**
+
+**Input:** s = ["H","a","n","n","a","h"]
+**Output:** ["h","a","n","n","a","H"]
+
+#### Constraints
+
+-   `1 <= s.length <= 105`
+-   `s[i]` is a [printable ascii character](https://en.wikipedia.org/wiki/ASCII#Printable_characters).
+
+### Thoughts
+
+> [!summary]
+> This is a #recursion problem, also can be solved using iteration.
+
+#### Base case:
+- size <= 1
+#### Pseudo code:
+
+- swap two ends
+- recurse the sub string(without the ends)
+
+### Solution
+
+Iteration
+```cpp
+class Solution {
+public:
+  void reverseString(vector<char> &s) {
+    int l = 0, r = s.size() - 1;
+
+    while (l < r) {
+      swap(s[l], s[r]);
+
+      l++;
+      r--;
+    }
+  }
+};
+```
+
+Recursion
+```cpp
+class Solution {
+  void reverse(vector<char> &s, int l, int r) {
+    if (l >= r) {
+      return;
+    }
+
+    swap(s[l++], s[r--]);
+    reverse(s, l, r);
+  }
+
+public:
+  void reverseString(vector<char> &s) { reverse(s, 0, s.size() - 1); }
+};
+```