commit changes to gh-pages aug 30

tg123 · tg123 · commit f945e888a0a1 · 2014-08-30T01:11:39.000+08:00
diff --git a/_includes/_root/permutation-sequence/README.md b/_includes/_root/permutation-sequence/README.md
@@ -1,4 +1,132 @@
+## [Factorial number system](http://en.wikipedia.org/wiki/Factorial_number_system#Permutations)
 
-## TODO 
-  * write down thinking
+It has to master this technology to find `kth` permutation or time limited.
 
+## Detail steps
+
+using wikipedia example
+
+2982th permutation of `[1, 2, 3, 4, 5, 6, 7]`.
+
+### Convert `k` to factorial based number
+
+```
+k = 2982
+n = 7
+```
+
+start form `n - 1`
+
+```
+2982 / 6! = 4 and remainder 102     |  4
+102  / 5! = 0 and remainder 102     |  0
+102  / 4! = 4 and remainder 6       |  4
+6    / 3! = 1 and remainder 0       |  1
+0    / 2! = 0 and remainder 0       |  0
+0    / 1! = 0 and remainder 0       |  0
+0    / 0! = 0 and remainder 0       |  0
+```
+
+So, `2982(10base) = 4041000(!base)`
+
+### Recover factorial based number to permutation.
+
+```
+
+
+
+index:  0  1  2  3  4  5  6
+chars: [1, 2, 3, 4, 5, 6, 7]
+final: []
+
+
+number: 4041000
+        ^
+        |
+
+Move chars[4] to the end of final
+
+
+chars: [1, 2, 3, 4, 5, 6, 7]  BEFORE
+index:  0  1  2  3  4  5, 6
+final: [5]
+chars: [1, 2, 3, 4, 6, 7]     AFTER
+
+
+number: 4041000
+         ^
+         |
+
+Move chars[0] to the end of final
+
+chars: [1, 2, 3, 4, 6, 7]     BEFORE
+index:  0  1  2  3  4  5
+final: [5, 1]
+chars: [2, 3, 4, 6, 7]        AFTER
+
+number: 4041000
+          ^
+          |
+
+Move chars[4] to the end of final
+
+chars: [2, 3, 4, 6, 7]       BEFORE
+index:  0  1  2  3  4
+final: [5, 1, 7]
+chars: [2, 3, 4, 6]          AFTER
+
+
+
+number: 4041000
+           ^
+           |
+
+Move chars[1] to the end of final
+
+chars: [2, 3, 4, 6]          BEFORE
+index:  0  1  2  3
+final: [5, 1, 7, 3]
+chars: [2, 4, 6]             AFTER
+
+
+
+number: 4041000
+            ^
+            |
+
+Move chars[0] to the end of final
+
+chars: [2, 4, 6]             BEFORE
+index:  0  1  2
+final: [5, 1, 7, 3, 2]
+chars: [4, 6]                AFTER
+
+
+
+number: 4041000
+             ^
+             |
+
+Move chars[0] to the end of final
+
+chars: [4, 6]                BEFORE
+index:  0  1
+final: [5, 1, 7, 3, 2, 4]
+chars: [6]                   AFTER
+
+
+number: 4041000
+              ^
+              |
+
+Move chars[0] to the end of final
+
+chars: [6]                   BEFORE
+index:  0
+final: [5, 1, 7, 3, 2, 4, 6]
+chars: []                    AFTER
+
+
+```
+
+The 2982th permutation of `[1, 2, 3, 4, 5, 6, 7]` is `[5, 1, 7, 3, 2, 4, 6]`
diff --git a/permutation-sequence/index.md b/permutation-sequence/index.md
@@ -1,7 +1,8 @@
 ---
 layout: solution
 title: Permutation Sequence
-date: 2014-07-23 02:42:48 +0800
+date: 2014-08-29 20:57:36 +0800
+eaten: true
 ---
 {% assign leetcode_name = {{page.path | remove: '/index.md'}}  %}
 {% assign leetcode_readme = {{leetcode_name | append: '/README.md' | prepend: '_root/' }}  %}
