commit changes to gh-pages aug 19

Author: tg123

_includes/_root/longest-palindromic-substring/README.md

@@ -1,4 +1,67 @@
+## Leetcode Blog Version
 
-## TODO 
-  * write down thinking
+Here is the [Leetcode Blog Version](http://leetcode.com/2011/11/longest-palindromic-substring-part-i.html). 
+This is a classic problem. I write my first leetcode accepted version based on that.
 
+
+## My own words version
+
+Brute force + isPalindromic will run out of time.
+
+### Recursive
+
+ * `length 1 substring`: all are palindromic
+ * `length 2 substring`: only if two char are same
+
+What if `length 3`
+
+```
+
+length 3 = length 1 + two char
+
+0 1 2 3 4
+a b c b a
++   ^    
+|   |
++---+    
+
+
+0 1 2 4 4
+a b c b a
+  +   ^     
+  |   |
+  +---+    
+
+```
+
+ * `length n` = inner `length n - 2` is palindromic AND (first char == last char)
+
+
+### Store `length n` into `P[lenght n][start index]`
+
+ * `P[1][3] = true` means that the substring starts from index 3 and 1 char long is palindromic.
+ * `P[5][2] = true` means that the substring starts from index 2 and 5 char long is NOT palindromic.
+
+
+a matrix for `abcba`
+
+```
+
+  0 1 2 3 4
+  a b c b a
+1 1 1 1 1 1
+2 0 0 0 0 -
+3 0 1 0 - -
+4 0 0 - - -
+5 1 - - - -
+^
+l
+e
+n
+
+```
+
+With the matrix, we can fill up the martix by `P[len][i] = P[len -2][i + 1] && S[i] == S[i + len -1]`.
+
+
+Note: the `length 0` is useless, so just using `P[len - 1]` for `len`.

_includes/_root/longest-palindromic-substring/Solution.java

@@ -1,43 +1,40 @@
 public class Solution {
     public String longestPalindrome(String s) {
 
+        char[] S = s.toCharArray();
 
-        // http://leetcode.com/2011/11/longest-palindromic-substring-part-i.html
+        if(S.length == 0) return "";
 
-        final char[] S = s.toCharArray();
-        final int N = S.length;
+        boolean[][] P = new boolean[S.length][S.length];
 
-        if(N == 0) return "";
-        if(N == 1) return s;
-        if(N == 2) return S[0] == S[1] ? s : "";
+        int maxi = 0;
+        int maxlen = 1;
 
-        boolean[][] P = new boolean[N][N];
+        // len 1
+        Arrays.fill(P[1 - 1], true);
 
-        for(int i = 0; i < N - 1; i++){
-            P[i][i] = true;
-            P[i][i + 1] = S[i] == S[i + 1];
-        }
-        
-        P[N - 1][N - 1] = true;
-        
-        for(int j = 2; j < N; j++){
-            for(int i = 0; i < j; i++){
-                P[i][j] |= P[i + 1][j - 1] && S[i] == S[j];
+        // len 2
+        for(int i = 0; i < S.length - 1; i++){
+            if(S[i] == S[i + 2 - 1]){
+                P[2 - 1][i] = true;
+                maxi = i;
+                maxlen = 2;
             }
         }
 
-        int mi = 0;
-        int mj = 0;
-        
-        for(int i = 0; i < N; i++){
-            for(int j = 0; j < N; j++){
-                if(P[i][j] && (j - i > mj - mi)){
-                    mi = i;
-                    mj = j;
+        // len 3 to max
+        for(int len = 3; len <= S.length; len++){
+            
+            for(int i = 0; i < S.length - (len - 1); i++){
+                
+                if(P[len - 1 - 2][i + 1] && S[i] == S[i + len - 1]){
+                    P[len - 1][i] = true;
+                    maxi = i;
+                    maxlen = len;
                 }
             }
-        }        
+        }
 
-        return new String(S, mi, mj - mi + 1);
+        return s.substring(maxi, maxi + maxlen);
     }
-}
+}

_includes/_root/palindrome-partitioning/README.md

@@ -1,4 +1,9 @@
+## Recursion 
 
-## TODO 
-  * write down thinking
+```
+i = 0 .. end
+
+partition(s) = s[0..i] + partition(s[i+1 .. end]) if s[0..i] is palindromic
+
+```
 

longest-palindromic-substring/index.md

@@ -1,7 +1,8 @@
 ---
 layout: solution
 title: Longest Palindromic Substring
-date: 2014-07-23 02:42:48 +0800
+date: 2014-08-18 17:56:19 +0800
+eaten: true
 ---
 {% assign leetcode_name = {{page.path | remove: '/index.md'}}  %}
 {% assign leetcode_readme = {{leetcode_name | append: '/README.md' | prepend: '_root/' }}  %}

palindrome-partitioning/index.md

@@ -1,7 +1,8 @@
 ---
 layout: solution
 title: Palindrome Partitioning
-date: 2014-07-23 02:42:48 +0800
+date: 2014-08-18 23:49:32 +0800
+eaten: true
 ---
 {% assign leetcode_name = {{page.path | remove: '/index.md'}}  %}
 {% assign leetcode_readme = {{leetcode_name | append: '/README.md' | prepend: '_root/' }}  %}