leetcode:344. Reverse String

Write a function that takes a string as input and returns the string reversed.

Example:
Given s = "Hello", Return "Olleh".

The main idea is to give a string, get the reverse string

Corner case: empty string or string length of 0

Solution One:

Request extra space, index points to the end of the original string, and constructs a new string in reverse sequence

 Public classSolution { Publicstring reversestring (string s) {if(s = =NULL|| S.length () = = 0)        {            returns; } String Res= ""; intindex = S.length ()-1;  for(; index >= 0; index--) {res+=S.charat (index); }                returnRes; }}

Complexity of Time: N, Spatial complexity: N
Timeout

Solution Two:

Double pointer point to tail, directly swap characters. No extra space required, only loop N/2 times

 Public classSolution { Publicstring reversestring (string s) {if(s = =NULL|| S.length () = = 0)        {            returns; }                intleft = 0; intright = S.length ()-1; Char[] Schar =S.tochararray ();  while(Left <Right ) {            Chartemp =Schar[left]; Schar[left]=Schar[right]; Schar[right]=temp; Left++; Right--; }                return NewString (Schar); }}

leetcode:344. Reverse String