Question

我有以下程序，用于检测带有边（单边）和边集（边集）的无向图中的周期。还有两个参数，left_set（用于存储要传递到递归的必要边）和循环（这是一个布尔值，最终确定图是否是循环的。

由于某种原因，检测在第一次递归后不起作用。以下是包含解释详细信息的注释的代码：

我在MYSQL中实现了以下功能（以避免混淆）：

-concat_set（）：如果是空集，则返回两个集合并置错误的'，'的连接

-remove_first（）：从集合

中删除第一个成员

-get_left_node（）/ get_right_node：返回边的节点，边之间的分隔符为'：'，因此边缘看起来像'12：15'

CREATE PROCEDURE `is_cyclic`(
IN `singleedge` VARCHAR(15), 
IN `edgeset` VARCHAR(1024), 
IN 'left_set' VARCHAR(512), 
OUT `cyclic` BOOLEAN)

BEGIN
DECLARE se_left VARCHAR(5);
DECLARE es_left VARCHAR(5);
DECLARE se_right VARCHAR(5);
DECLARE es_right VARCHAR(5);
Call get_left_node(singleedge, se_left);
Call get_left_node(SUBSTRING_INDEX(edgeset, ',', 1), es_left);
Call get_right_node(singleedge, se_right);
Call get_right_node(SUBSTRING_INDEX(edgeset, ',', 1), es_right);



--is edgeset emptY?
    IF LENGTH(edgeset)= 0 AND LENGTH(left_set) = 0 THEN
        BEGIN

            SET cyclic= false;

        END;    

--are singeeledge and first edge in edgeset the same?        
    ELSEIF ((se_left = es_left
        OR se_left= es_right)
        AND( se_right = es_left
        OR se_right = es_right)) THEN
                    BEGIN
            set cyclic= true;
                        END;


--do singleedge and first edge in edgeset share any vertices?       
    ELSEIF se_left = es_left 
        OR se_left= es_right
        OR se_right = es_left
        OR se_right = es_right
        THEN
        --check for all possiblities
            BEGIN

                --if left vertex of singleedge and left vertex of current edge in front of edgeset are the same               
                IF se_left=es_left THEN
                                    BEGIN
                                    --test if the edge of combined uncommon vertices (forming concat(se_right,':',es_right)) exists in the remaining edgeset concatanated with the left_set
                                    CALL is_cyclic(concat(se_right,':',es_right),concat_set(left_set,remove_first(edgeset)), '', cyclic);
                                    --if the recursion returns cyclic=false, then remove the considered edge from edgeset and continue trying to match the original singleedge with the rest of edgeset
                                     IF cyclic=false THEN
                                        CALL is_cyclic(singleedge, remove_first(edgeset), left_set, cyclic);
                                      END IF;
                                     END;
                ELSEIF se_left= es_right THEN
                                    BEGIN
                                    CALL is_cyclic(concat(se_right,':',es_left), concat_set(left_set, remove_first(edgeset)), '', cyclic);
                                    IF cyclic=false THEN
                                        CALL is_cyclic(singleedge, remove_first(edgeset), left_set, cyclic);
                                     END IF;
                                     END;
                ELSEIF se_right=es_left THEN
                                    BEGIN
                                    CALL is_cyclic(concat(se_left,':',es_right), concat_set(left_set, remove_first(edgeset)), '', cyclic);
                                    IF cyclic=false THEN
                                        CALL is_cyclic(singleedge, remove_first(edgeset), left_set, cyclic);
                                    END IF;
                                    END;
                ELSE
                                    BEGIN
                                    CALL is_cyclic(concat(se_left,':',es_left), concat_set(left_set, remove_first(edgeset)), '', cyclic);
                                    IF cyclic=false THEN
                                        CALL is_cyclic(singleedge, remove_first(edgeset), left_set, cyclic);
                                    END IF;  
                                      END;
                                END IF;


            END;    


        ELSE
            BEGIN
                --if the current edge being considered from the edgeset does not contain any vertex in common with singleedge, set it aside into left_set and call is_cyclic recurisvely with the edge removed
                SET left_set = concat_set(left_set, SUBSTRING_INDEX(edgeset, ',', 1));
                CALL is_cyclic(singleedge, remove_first(edgeset), left_set, cyclic);
                END;

    END IF;
END

Answer 1

尝试重置此mysql变量：max_sp_recursion_depth，thread_stack

SET SESSION max_sp_recursion_depth = 10;
SET SESSION thread_stack = 250000;

执行上述命令后，调用您的程序。连续执行两个语句。根据您的要求增加 thread_stack 变量的大小。

MySQL递归周期检测程序

1 个答案: