| ALGORITHM: patternGrowth () |
| INPUT: (1) : prefix sequence pattern. |
| OUTPUT: the set of gap-constrained closed sequential |
| patterns with prefix . |
| (14)backward_check (P needPruning, hasBackwardExtension) |
| (15)if (needPruning) |
| (16)return; |
| (17)forward_check(, hasForwardExtension); |
| (18)if ! (hasBackwardExtension ∣∣ hasForwardExtension) |
| (19)output pattern ; |
| (20)search each forward space of all appearances of , and |
| find the set of all local frequent items, ; |
| (21)for each item in |
| (22)build new pattern = + ; |
| (23)call patternGrowth (); |
| (24)return. |