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Commitb663bc8

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commit changes to gh-pages aug 19
1 parent49470f2 commitb663bc8

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Lines changed: 65 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,67 @@
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##Leetcode Blog Version
12

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##TODO
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*writedown thinking
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Here is the[Leetcode Blog Version](http://leetcode.com/2011/11/longest-palindromic-substring-part-i.html).
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This is a classic problem. Iwritemy first leetcode accepted version based on that.
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##My own words version
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Brute force + isPalindromic will run out of time.
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###Recursive
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*`length 1 substring`: all are palindromic
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*`length 2 substring`: only if two char are same
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What if`length 3`
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```
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length 3 = length 1 + two char
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0 1 2 3 4
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a b c b a
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+ ^
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| |
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+---+
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0 1 2 4 4
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a b c b a
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+ ^
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| |
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+---+
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```
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*`length n` = inner`length n - 2` is palindromic AND (first char == last char)
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###Store`length n` into`P[lenght n][start index]`
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*`P[1][3] = true` means that the substring starts from index 3 and 1 char long is palindromic.
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*`P[5][2] = true` means that the substring starts from index 2 and 5 char long is NOT palindromic.
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a matrix for`abcba`
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```
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0 1 2 3 4
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a b c b a
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1 1 1 1 1 1
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2 0 0 0 0 -
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3 0 1 0 - -
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4 0 0 - - -
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5 1 - - - -
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^
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l
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e
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n
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```
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With the matrix, we can fill up the martix by`P[len][i] = P[len -2][i + 1] && S[i] == S[i + len -1]`.
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Note: the`length 0` is useless, so just using`P[len - 1]` for`len`.
Lines changed: 25 additions & 28 deletions
Original file line numberDiff line numberDiff line change
@@ -1,43 +1,40 @@
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publicclassSolution {
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publicStringlongestPalindrome(Strings) {
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char[]S =s.toCharArray();
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// http://leetcode.com/2011/11/longest-palindromic-substring-part-i.html
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if(S.length ==0)return"";
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finalchar[]S =s.toCharArray();
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finalintN =S.length;
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boolean[][]P =newboolean[S.length][S.length];
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if(N ==0)return"";
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if(N ==1)returns;
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if(N ==2)returnS[0] ==S[1] ?s :"";
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intmaxi =0;
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intmaxlen =1;
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boolean[][]P =newboolean[N][N];
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// len 1
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Arrays.fill(P[1 -1],true);
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for(inti =0;i <N -1;i++){
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P[i][i] =true;
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P[i][i +1] =S[i] ==S[i +1];
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}
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P[N -1][N -1] =true;
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for(intj =2;j <N;j++){
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for(inti =0;i <j;i++){
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P[i][j] |=P[i +1][j -1] &&S[i] ==S[j];
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// len 2
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for(inti =0;i <S.length -1;i++){
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if(S[i] ==S[i +2 -1]){
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P[2 -1][i] =true;
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maxi =i;
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maxlen =2;
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}
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}
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intmi =0;
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intmj =0;
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for(inti =0;i <N;i++){
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for(intj =0;j <N;j++){
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if(P[i][j] && (j -i >mj -mi)){
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mi =i;
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mj =j;
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// len 3 to max
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for(intlen =3;len <=S.length;len++){
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for(inti =0;i <S.length - (len -1);i++){
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if(P[len -1 -2][i +1] &&S[i] ==S[i +len -1]){
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P[len -1][i] =true;
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maxi =i;
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maxlen =len;
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}
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}
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}
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}
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returnnewString(S,mi,mj -mi +1);
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returns.substring(maxi,maxi +maxlen);
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}
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}
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}
Lines changed: 7 additions & 2 deletions
Original file line numberDiff line numberDiff line change
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##Recursion
12

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##TODO
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* write down thinking
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```
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i = 0 .. end
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partition(s) = s[0..i] + partition(s[i+1 .. end]) if s[0..i] is palindromic
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```
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‎longest-palindromic-substring/index.md

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---
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layout:solution
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title:Longest Palindromic Substring
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date:2014-07-23 02:42:48 +0800
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date:2014-08-18 17:56:19 +0800
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eaten:true
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---
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{% assign leetcode_name = {{page.path | remove: '/index.md'}} %}
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{% assign leetcode_readme = {{leetcode_name | append: '/README.md' | prepend: '_root/' }} %}

‎palindrome-partitioning/index.md

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---
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layout:solution
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title:Palindrome Partitioning
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date:2014-07-23 02:42:48 +0800
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date:2014-08-18 23:49:32 +0800
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eaten:true
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---
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{% assign leetcode_name = {{page.path | remove: '/index.md'}} %}
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{% assign leetcode_readme = {{leetcode_name | append: '/README.md' | prepend: '_root/' }} %}

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