459. Repeated Substring Pattern
Easy
Given a non-empty string check if it can be constructed by taking a substring of it and appending multiple copies of the substring together. You may assume the given string consists of lowercase English letters only and its length will not exceed 10000.
Example 1:
Input: "abab" Output: True Explanation: It's the substring "ab" twice.
Example 2:
Input: "aba" Output: False
Example 3:
Input: "abcabcabcabc" Output: True Explanation: It's the substring "abc" four times. (And the substring "abcabc" twice.)
package leetcode.easy;
public class RepeatedSubstringPattern {
public boolean repeatedSubstringPattern(String s) {
// corner case
if (s == null || s.length() == 0) {
return true;
}
int n = s.length();
for (int len = n / 2; len >= 1; len--) {
if (n % len != 0) {
continue; // s length must can be divided by the pattern length
} else {
String pattern = s.substring(0, len); // pattern string
int i = len; // start index of 2nd pattern
int j = i + len - 1; // end index of 2nd pattern
while (j < n) {
String substr = s.substring(i, j + 1);
if (!pattern.equals(substr)) {
break; // failed for this pattern, try next pattern
} else {
i += len;
j += len;
}
}
// if it past the last substring check, i will be n
if (i == n) {
return true;
}
}
}
return false;
}
@org.junit.Test
public void test() {
System.out.println(repeatedSubstringPattern("abab"));
System.out.println(repeatedSubstringPattern("aba"));
System.out.println(repeatedSubstringPattern("abcabcabcabc"));
}
}