Rotate string left

Description:

In assembly language, there is a shift instruction called ROL. Now a simple task is to simulate the operation result of this instruction using strings. For a given Character Sequence S, please shift its loop left K-bit sequence output. For example, the Character Sequence S = "abcxyzdef" requires that the output result of the loop be shifted three places left, that is, "xyzdefabc ". Is it easy? OK, get it done!

Input:

Multiple groups of test data. Each test data contains a Character Sequence s and a non-negative integer k. The length of S cannot exceed 1000.

Output:

Output a new sequence for each test case.

Package test21; import Java. util. extends; public class main {public static void main (string [] ARGs) {extends = new loads (system. in); While (partial. hasnext () {string STR = success. next (); int n = random. nextint (); system. out. println (revstring (STR, n) ;}/ *** ①: Pay attention to the N value. Because it is a cyclic shift, you can use the remainder method ②: using stringbuffer: to improve performance ** ③: Using substring (beginindex, endindex) to simplify computing * Performance Analysis: time complexity is O (n) --- substring; space complexity Degree is O (n) --- stringbuffer ** @ Param Str * @ Param N * @ return */public static string reverse (string STR, int N) {stringbuffer = new stringbuffer (); int length = Str. length (); int M = n % length; If (M <0) {return STR ;}// you can directly split the substring, then splice the split substrings into stringbuffer. append (Str. substring (M, str. length ())). append (Str. substring (0, M); Return stringbuffer. tostring ();}/*** thought: we still think of the string as composed of two segments, and remember XY. * The left rotation is equivalent to converting the string XY to Yx. We first define a flip operation on the string, * That is, the character order in the flip string. After turning X, record it as XT. Obviously (XT) t = x. ** First, we perform the flip operation on the X and Y segments respectively to obtain the xtyt. * Perform the xtyt flip operation to obtain (xtyt) t = (yt) T (XT) t = Yx. * This is exactly the expected result. * ①: First, the first half is in reverse order. * ②: Then the second half is in reverse order. * ③: Then, the whole is in reverse order. * performance analysis: the time complexity is O (n ), the space complexity is O (1) ** @ Param Str * @ Param N * @ return */public static string revstring (string STR, int N) {If (Str. length () = 0) {return STR;} Char [] C = Str. tochararray (); int M = n % Str. length (); // flip (0, m) characters int firsta = 0, lasta = m-1; while (firsta <lasta) {char temp = C [firsta]; C [firsta] = C [lasta]; C [lasta] = temp; firsta ++; lasta --;} // then (M, str. length flip) int firstb = m, lastb = Str. length ()-1; while (firstb <lastb) {char temp = C [firstb]; C [firstb] = C [lastb]; C [lastb] = temp; firstb ++; lastb --;} // flip all strings to int firstc = 0, lastc = Str. length ()-1; while (firstc <lastc) {char temp = C [firstc]; C [firstc] = C [lastc]; C [lastc] = temp; firstc ++; lastc --;} return new string (c );}}

Rotate string left