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Copy pathP_214.java
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25 lines (22 loc) · 771 Bytes
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package leetcode.hard;
public class P_214 {
public String shortestPalindrome(String s) {
final StringBuilder reverse = new StringBuilder(s).reverse();
final int[] kmp = kmp(s + '#' + reverse);
return new StringBuilder(s.substring(kmp[kmp.length - 1])).reverse().append(s).toString();
}
private static int[] kmp(String s) {
final int n = s.length();
final int[] prefixSuffix = new int[n];
for (int i = 1, j = 0; i < s.length(); i++) {
while (j > 0 && s.charAt(i) != s.charAt(j)) {
j = prefixSuffix[j - 1];
}
if (s.charAt(i) == s.charAt(j)) {
j++;
}
prefixSuffix[i] = j;
}
return prefixSuffix;
}
}