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