796. Rotate String

// LeetCode URL: https://leetcode.com/problems/rotate-string/
/**
 * All rotations of A are contained in A+A
 *
 * Time Complexity: O(N^2)
 *
 * Space Complexity: O(N)
 *
 * N = Length of input string A or B
 */
class Solution1 {
    public boolean rotateString(String A, String B) {
        if (A == null || B == null || A.length() != B.length()) {
            return false;
        }

        return (A + A).contains(B);
    }
}

/**
 * All rotations of A are contained in A+A. Using KMP for checking contains.
 *
 * Time Complexity: O(N)
 *
 * Space Complexity: O(N)
 *
 * N = Length of input string A or B
 */
class Solution {
    public boolean rotateString(String A, String B) {
        if (A == null || B == null || A.length() != B.length()) {
            return false;
        }
        if (A.length() == 0) {
            return true;
        }

        int[] lookupTable = genLookupTable(B);

        return contains(A + A, B, lookupTable);
    }

    private int[] genLookupTable(String s) {
        int[] table = new int[s.length()];
        int i = 1;
        int index = 0;
        while (i < s.length()) {
            if (s.charAt(i) == s.charAt(index)) {
                index++;
                table[i] = index;
                i++;
            } else {
                if (index > 0) {
                    index = table[index - 1];
                } else {
                    i++;
                }
            }
        }
        return table;
    }

    private boolean contains(String haystack, String needle, int[] lookupTable) {
        int i = 0;
        int j = 0;
        while (i < haystack.length() && j < needle.length()) {
            if (haystack.charAt(i) == needle.charAt(j)) {
                i++;
                j++;
            } else {
                if (j > 0) {
                    j = lookupTable[j - 1];
                } else {
                    i++;
                }
            }
        }

        if (j == needle.length()) {
            return true;
        } else {
            return false;
        }
    }
}