796 Rotate String

We are given two strings,AandB.

A_shift onA_consists of taking stringAand moving the leftmost character to the rightmost position. For example, ifA = 'abcde', then it will be'bcdea'after one shift onA. ReturnTrueif and only ifAcan becomeBafter some number of shifts onA.

Example 1:
Input: A = 'abcde', B = 'cdeab'
Output: true

Example 2:
Input: A = 'abcde', B = 'abced'
Output: false

Note:

• AandBwill have length at most100.

这题在cc189见过，如果是合法的rotattion的话，那个把原来的string连起来，那个rotate了的string会是那个的substring。例如：abcdeabcde里会有cdeab，如果不是合法的就不会是substring

public boolean rotateString(String A, String B) {
    if (A == null || B == null) {
        return true;
    } else if (A.length() != B.length()) {
        return false;
    }

    String total = A + A;
    return total.indexOf(B) != -1;
}