Rotate String

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Rotate String

旋转string

Given a string and an offset, rotate string by offset. (rotate from left to right)

Example

Given "abcdefg"

for offset=0, return "abcdefg"

for offset=1, return "gabcdef"

for offset=2, return "fgabcde"

for offset=3, return "efgabcd"

Solution:

    public char[] rotateString(char[] A, int offset) {        if (A == null) {            return null;        }        char[] result = new char[A.length];        if (A.length == 0) {            return result;        }        offset = offset % A.length;        int i;        int j;        for (i = 0, j = A.length - offset; i < offset; i++, j++) {            result[i] = A[j];        }        for (j = 0; j < A.length - offset; i++, j++) {            result[i] = A[j];        }        return result;    }

    public char[] rotateString(char[] A, int offset) {        if (A == null) {            return null;        }        char[] result = new char[A.length];        if (A.length == 0) {            return result;        }        offset = offset % A.length;        System.arraycopy(A, A.length - offset, result, 0, offset);        System.arraycopy(A, 0, result, offset, A.length - offset);        return result;    }

    public char[] rotateString(char[] A, int offset) {        if(A == null|| A.length <= 1) {            return A;        }        offset = offset % A.length;        if(offset <= 0) {            return A;        }        //0123456        //abcdefg        reverse(A, A.length - offset, A.length - 1);        reverse(A, 0, A.length - offset - 1);        reverse(A, 0, A.length - 1);        return A;    }    private void reverse(char[] A, int start, int end) {        for(int i = start, j = end; i < j; i++,j--) {            char temp = A[i];            A[i] = A[j];            A[j] = temp;        }    }

思路：

双index用起来方便。一段是0到A.length - offset - 1, 一段是A.length - offset到A.length - 1. 先把后一段拷贝，在把前一段拷贝。

使用System.arraycopy(src, SrcStart, dest, DestStart, len)实现数组拷贝。

三步翻转法。一定是段内有序。

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