796. Rotate String

Problem

Given two strings s and goal, return true if and only if s can become goal **after some number of *shifts* on** s.

A shift on s consists of moving the leftmost character of s to the rightmost position.

• For example, if s = "abcde", then it will be "bcdea" after one shift.

  Example 1:

Input: s = "abcde", goal = "cdeab"
Output: true

Example 2:

Input: s = "abcde", goal = "abced"
Output: false

  Constraints:

• 1 <= s.length, goal.length <= 100

• s and goal consist of lowercase English letters.

Solution (Java)

class Solution {
    private boolean check(String s, String goal, int i) {
        int j = 0;
        int len = goal.length();
        while (j < len) {
            if (i == len) {
                i = 0;
            }
            if (s.charAt(i) != goal.charAt(j)) {
                return false;
            }
            j++;
            i++;
        }
        return true;
    }

    public boolean rotateString(String s, String goal) {
        if (s.length() != goal.length()) {
            return false;
        }
        int len = s.length();
        if (s.charAt(0) == goal.charAt(0) && !s.equals(goal)) {
            return false;
        }
        for (int i = 0; i < len; i++) {
            if (s.charAt(i) == goal.charAt(0) && check(s, goal, i)) {
                return true;
            }
        }
        return false;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).