题目：
提交01： 目标先实现功能
1 class Solution { 2 public String longestPalindrome(String s) { 3 char[] ch = s.toCharArray(); 4 if(ch.length==0){ 5 return ""; 6 } 7 int left = 0; 8 int right = 0; 9 int index = 0; 10 int j =0; 11 int k=0; 12 for(int i=1;i<ch.length;i++){ 13 while(index<i){ 14 for(j=index,k=0;j<=i-k;j++,k++){ 15 if(ch[j] != ch[i-k]){ 16 break; 17 } 18 } 19 if(j>=i-k){ 20 if(i-index>right-left) { 21 left = index; 22 right = i; 23 } 24 } 25 index++; 26 } 27 index = 0; 28 } 29 30 StringBuffer stringBuffer = new StringBuffer(); 31 while(left<=right) { 32 stringBuffer.append(ch[left]); 33 left++; 34 } 35 return stringBuffer.toString(); 36 } 37 }
很明显，耗时太严重，现在考虑如何优化？？
提交02： 优化
1 class Solution { 2 3 public String longestPalindrome(String s) { 4 if(s==null||s.equals("")){ 5 return ""; 6 } 7 int low =0; 8 int high =0; 9 int tempLow =0; 10 int tempHigh = 0; 11 char[] ch = s.toCharArray(); 12 for(int i=0;i<ch.length;i++){ 13 tempLow = i; 14 tempHigh = i; 15 while(tempHigh<ch.length-1&&ch[tempHigh+1]==ch[tempLow]){ 16 tempHigh++; 17 } 18 //i=tempHigh; 19 while(tempLow>0&&tempHigh<ch.length-1&&ch[tempLow-1]==ch[tempHigh+1]){ 20 tempLow--; 21 tempHigh++; 22 } 23 if(high-low<tempHigh-tempLow){ 24 high = tempHigh; 25 low = tempLow; 26 } 27 28 } 29 return s.substring(low,high+1); 30 31 } 32 }
当讲 i = tempHigh 放开后
提交：03
1 class Solution { 2 3 public String longestPalindrome(String s) { 4 if(s==null||s.equals("")){ 5 return ""; 6 } 7 int low =0; 8 int high =0; 9 int tempLow =0; 10 int tempHigh = 0; 11 char[] ch = s.toCharArray(); 12 for(int i=0;i<ch.length;i++){ 13 tempLow = i; 14 tempHigh = i; 15 while(tempHigh<ch.length-1&&ch[tempHigh+1]==ch[tempLow]){ 16 tempHigh++; 17 } 18 i=tempHigh; 19 while(tempLow>0&&tempHigh<ch.length-1&&ch[tempLow-1]==ch[tempHigh+1]){ 20 tempLow--; 21 tempHigh++; 22 } 23 if(high-low<tempHigh-tempLow){ 24 high = tempHigh; 25 low = tempLow; 26 } 27 28 } 29 return s.substring(low,high+1); 30 31 } 32 }
极大的缩短了执行时间。
提交04 ： 优化
使用数组保存状态具有轻微优化
1 class Solution { 2 3 public String longestPalindrome(String s) { 4 if(s==null||s.equals("")){ 5 return ""; 6 } 7 int[] index = new int[2]; 8 int tempLow =0; 9 int tempHigh = 0; 10 char[] ch = s.toCharArray(); 11 for(int i=0;i<ch.length;i++){ 12 tempLow = i; 13 tempHigh = i; 14 while(tempHigh<ch.length-1&&ch[tempHigh+1]==ch[tempLow]){ 15 tempHigh++; 16 } 17 i=tempHigh; 18 while(tempLow>0&&tempHigh<ch.length-1&&ch[tempLow-1]==ch[tempHigh+1]){ 19 tempLow--; 20 tempHigh++; 21 } 22 if(index[1]-index[0]<tempHigh-tempLow){ 23 index[1] = tempHigh; 24 index[0] = tempLow; 25 } 26 27 } 28 return s.substring(index[0],index[1]+1); 29 30 } 31 }
