# Use the "use median sorting basis" to implement a tree structure (1)

Source: Internet
Author: User
In the compilation of BBS, people often ask how to implement the tree structure? The irresponsible answer is that recursive algorithms are used. Of course, recursion is a feasible method (binary tree calendars only seem to use recursive algorithms), but for BBS, in this case, a large number of SQL queries are required. (although stored procedures can be used, a faster algorithm should be considered to accelerate the speed ).
The following is a feasible algorithm for implementing the tree structure of complete screen discard.
?? The following provides another tree structure using the "using the median sort basis:
I. Main idea: add an ordernum sorting base field and return the value of ordernum in the same root post to the value of ordernum.
?? For concise description, only fields related to the tree structure are discussed here.
Add three redundant fields to the table. The "rootid" field is used to record the root id, the "deep" field is used to record the depth of the reply (when it is 0, it indicates the root paste), and the "ordernum" column is used to record the base of the sort ).
Table forum and (only columns related to the tree structure ):
Id? Rootid? Deep ?? Ordernum
Among them, id, rootid, and deep are int type (deep can be tinyint type), and ordernum is float type.
Example: (for simplicity, a small starting base should be used. In practice, a large starting base should be used and an integer power of 2 should be used, for example, 65536 = 2 ^ 16, the sorting mentioned below refers to sorting by ordernum from small to large ).
Id? Rootid ?? Deep ?? Ordernum
1 ??? 0 ???? 0 ?????? 0
2 ??? 1 ???? 1 ????? 64
______________________________
3 ??? 1 ???? 1 ????? 32 ?? Reply to the 1st post, and take the value of the base number 1 and 2 (0 + 64)/2
The sorting result is as follows:
Id? Rootid ?? Deep ?? Ordernum
1 ??? 0 ???? 0 ?????? 0
3 ??? 1 ???? 1 ????? 32
2 ??? 1 ???? 1 ????? 64
______________________________
4 ??? 1 ???? 2 ????? 48? Reply to the 3rd post, and obtain the base value of 3 and 2 (32 + 64)/2
The sorting result is as follows:
Id? Rootid ?? Deep ?? Ordernum
1 ??? 0 ???? 0 ?????? 0
3 ??? 1 ???? 1 ????? 32
4 ??? 1 ???? 2 ????? 48
2 ??? 1 ???? 1 ????? 64
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