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lps.java
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94 lines (92 loc) · 2.7 KB
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package LongestPalindromicSubstring005;
/**
* Created by Administrator on 2017/8/9.
*/
public class lps {
//方法1
/*public String longestPalindrome(String s){
if (s == null||s.length()==0){
return "";
}
int length=s.length();
int max=0;
String result = "";
for(int i=1;i<=2*length-1;i++){
int count=1;
while(i-count>=0&&i+count<=2*length&&getChar(s,i-count)==getChar(s,i+count)){
count++;
}
count--;
if(count>max){
result=s.substring((i-count)/2,(i+count)/2);
max=count;
}
}
return result;
}
private char getChar(String s,int i){
if(i%2==0)
return '#';
else
return s.charAt(i/2);
}*/
//方法2
/*public String longestPalindrome(String s){
if(s==null||s.length()==0)
return "";
int max=0;
String res="";
for(int i=0;i<2*s.length()-1;i++){
int left=i/2;
int right=i/2;
if(i%2==1)
right++;
String str=lengthOfPalindrome(s,left,right);
if(max<str.length()){
max=str.length();
res=str;
}
}
return res;
}
private String lengthOfPalindrome(String s,int left,int right){
while(left>=0&&right<s.length()&&s.charAt(left)==s.charAt(right)){
left--;
right++;
}
return s.substring(left+1,right);
}*/
//方法3，动态规划DP,有问题
public String longestPalindrome(String s) {
int n = s.length();
int longestBegin = 0;
int maxLen = 1;
boolean[][] table = new boolean[n][n];
for (int i = 0; i < n; i++) {
table[i][i] = true;
}
for (int i = 0; i < n-1; i++) {
if (s.charAt(i) == s.charAt(i+1)) {
table[i][i+1] = true;
longestBegin = i;
maxLen = 2;
}
}
for (int len = 3; len <= n; len++) {
for (int i = 0; i < n-len+1; i++) {
int j = i+len-1;
if (s.charAt(i) == s.charAt(j) && table[i+1][j-1]) {
table[i][j] = true;
longestBegin = i;
maxLen = len;
}
}
}
return s.substring(longestBegin-1, maxLen);
}
public static void main(String[] args){
String s="babad";
String l=new lps().longestPalindrome(s);
System.out.print(l);
}
}