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Copy pathCenterExpansionAlgorithm.java
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74 lines (60 loc) · 2 KB
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package string;
import java.util.Random;
import java.util.UUID;
//最长回文字符串，中心阔山算法
public class CenterExpansionAlgorithm {
private static final String ALPHABET = "abcdefghijklmnopqrstuvwxyz";
public static String generateRandomString(int length) {
Random random = new Random();
StringBuilder sb = new StringBuilder(length);
for (int i = 0; i < length; i++) {
int index = random.nextInt(ALPHABET.length());
char randomChar = ALPHABET.charAt(index);
sb.append(randomChar);
}
return sb.toString();
}
public static void main(String[] args) {
for (int i = 0; i < 20 ; i++) {
String s = generateRandomString(20);
System.out.println(s);
String s1 = new CenterExpansionAlgorithm().longestPalindrome(s);
System.out.println(s1);
}
}
//获取字符串最长回文
public String longestPalindrome(String s){
if(s == null || s.length() < 1){
return null;
}
int start = 0,end = 0,length = 0;
for (int i = 0; i < s.length(); i++) {
int i1 = expandAroundCenter(s, i, i);
int i2 = expandAroundCenter(s, i, i + 1);
//获取最大长度
length = Math.max(i1, i2);
if (length > end - start + 1){
start = i - (length - 1)/2;
end = i + length/2;
}
// if(end - start < length){
// start = i-(length/2);
// if(length % 2 == 0){
// start++;
// }
// end = start + length;
// }
}
return s.substring(start,end+1);
}
/**
* 环绕中心扩展
*/
public int expandAroundCenter(String s,int left,int right){
while (left >= 0 && right< s.length() && s.charAt(left) == s.charAt(right)){
left--;
right++;
}
return right - left -1;
}
}