1 package com.java.tencent;
 2 
 3 public class T_2_longestPalindrome {
 4 
 5     public String test1(String s){
 6         long startTime=System.currentTimeMillis();
 7         int len = s.length();
 8         int tmp = 0;
 9         String result = "";
10         for(int i=0;i<len;i++){
11             if(tmp+i-len>0){
12                 break;
13             }
14             int lenj = len-1;
15             for(int j=lenj;j>=i;j--){
16                 if(tmp>j-i+1){
17                     break;
18                 }
19                 String ch = s.substring(i,i+1);
20                 String chj = s.substring(j,j+1);
21                 if(ch.equals(chj)){
22                     String str = s.substring(i,j+1);
23                     if(tmp>str.length()){
24                         continue;
25                     }
26                     boolean bl = true;
27                     int ln = str.length();
28                     int lenm = ln/2+1;
29                     for(int m=0;m<lenm;m++){
30                         CharSequence start = str.subSequence(m, m+1);
31                         CharSequence end = str.subSequence(ln-m-1,ln-m);
32                         if(!start.equals(end)){
33                             bl = false;
34                             break;
35                         }
36                     }
37                     if(bl && ln>tmp){
38                         result = str;
39                         tmp = ln;
40                     }
41                 }
42             }
43         }
44         System.out.println(result);
45         long endTime=System.currentTimeMillis();
46         System.out.println("Program run time: "+(endTime-startTime)+"ms");
47         return result;
48     }
49 
50     public String test2(String s){
51         long startTime=System.currentTimeMillis();
52         int len = s.length();
53         int tmp = 0;
54         String result = "";
55         for(int i=0;i<len;i++){
56             if(tmp+i-len>0){
57                 break;
58             }
59             for(int j=len-1;j>=i;j--){
60                 if(tmp>j-i+1){
61                     break;
62                 }
63                 String str = s.substring(i,j+1);
64                 boolean bl = true;
65                 for(int m=0;m<(str.length()/2+1);m++){
66                     Character start = str.charAt(m);
67                     Character end = str.charAt(str.length()-m-1);
68                     if(!start.equals(end)){
69                         bl = false;
70                         break;
71                     }
72                 }
73                 if(bl && str.length()>tmp){
74                     result = str;
75                     tmp = str.length();
76                     break;
77                 }
78             }
79         }
80         System.out.println(result);
81         long endTime=System.currentTimeMillis();
82         System.out.println("Program run time: "+(endTime-startTime)+"ms");
83         return result;
84     }
85     
86     
87     public static void main(String[] args) {
88         T_2_longestPalindrome lp = new T_2_longestPalindrome();
89         String s = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaabcaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
90         lp.test2(s);
91     }
92 
93 }

A program that returns the longest palindrome substring (1000 a, palindrome string is such as abcddcba and bcb, the left and right sides are the same, of course, a is also a character). The previously used test1 always has an execution time of more than 500, and the time can never be reduced. Finally, the problem falls to the position of two truncated strings. After modification, test2 successfully reduces the execution time.

test1 uses sub to intercept string, execution time 500+ms

test2 uses charAt with execution time of 180ms

As can be seen above, the implementation efficiency is different.