"Leetcode" solution in Java--easy2

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6:reverse String

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

This topic: string reversal questions.

Idea: This problem in the first Class C + + time on the machine problem has been done, then the idea is: to convert a string to char[], from the end of the head to traverse a reverse order to copy the character to another array (from start to finish), and then the new array ToString (). Now in Java, replace the new array with StringBuffer, reverse-traverse char[] One by one append to buffer, then ToString (). Because each element is traversed once, the complexity O (n).

 Public string reversestring (string s) {        char[] chars=S.tochararray ();        StringBuffer buffer=new  stringbuffer ();                for (int i=chars.length-1;i>=0;--i) {            buffer.append (chars[i]);        }                 return buffer.tostring ();    }

The second way of thinking is: to char[the front and back half of the exchange can, just traverse half, the complexity of O (N/2).

  Publicstring reversestring (string s) {Char[] chars=S.tochararray (); intHalf=chars.length/2;  for(inti=0;ii) {            CharTemp=chars[chars.length-1-i]; Chars[chars.length-1-i]=Chars[i]; Chars[i]=temp; }         //note here: char[] Conversion to string is implemented through new string (char[]).        return NewString (chars); }

"Leetcode" solution in Java--easy2