344 Reverse String 反转字符串
Description:
Write a function that reverses a string. The input string is given as an array of characters char[].
Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.
You may assume all the characters consist of printable ascii characters.
Example :
Example 1:
Input: ["h","e","l","l","o"]
Output: ["o","l","l","e","h"]
Example 2:
Input: ["H","a","n","n","a","h"]
Output: ["h","a","n","n","a","H"]
题目描述:
编写一个函数,其作用是将输入的字符串反转过来。输入字符串以字符数组 char[] 的形式给出。
不要给另外的数组分配额外的空间,你必须原地修改输入数组、使用 O(1) 的额外空间解决这一问题。
你可以假设数组中的所有字符都是 ASCII 码表中的可打印字符。
示例 :
示例 1:
输入:["h","e","l","l","o"]
输出:["o","l","l","e","h"]
示例 2:
输入:["H","a","n","n","a","h"]
输出:["h","a","n","n","a","H"]
思路:
- 双指针循环交换, 注意到交换的都是可打印字符串, 交换可以用异或进行
- 递归
时间复杂度O(n), 空间复杂度O(1)
代码:
C++:
class Solution
{
public:
void reverseString(vector<char>& s)
{
int i = 0, j = s.size() - 1;
while (i < j)
{
s[i] ^= s[j];
s[j] ^= s[i];
s[i++] ^= s[j--];
}
}
};
Java:
class Solution {
public void reverseString(char[] s) {
swap(0, s.length - 1, s);
}
public void swap(int start, int end, char[] s) {
if (start >= end) {
return;
}
char temp = s[start];
s[start] = s[end];
s[end] = temp;
swap(start + 1, end - 1, s);
}
}
Python:
class Solution:
def reverseString(self, s: List[str]) -> None:
"""
Do not return anything, modify s in-place instead.
"""
s.reverse()