-
Notifications
You must be signed in to change notification settings - Fork 0
/
HashAndRecursion.php
65 lines (52 loc) · 1.72 KB
/
HashAndRecursion.php
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
<?php
class Solution {
/**
* hash map already visiting nodes
*/
private $visiting = [];
/**
* hash map course pre requisites
*/
private $coursePrerequisites = [];
/**
* @param Integer $numCourses
* @param Integer[][] $prerequisites
* @return Boolean
*/
function canFinish($numCourses, $prerequisites) {
// reset all pre requisites list
for($course = 0; $course < $numCourses ; $course++){
$this->coursePrerequisites[$course] = [];
}
// set all course pre requisites
foreach($prerequisites as $course => $prerequisite){
$this->coursePrerequisites[$prerequisite[0]][] = $prerequisite[1];
}
// iterate over all courses and check
for($course = 0; $course < $numCourses ; $course++){
if(!$this->checkCourse($course)) return false ;
}
return true ;
}
/**
* @param Integer $course
* @return Boolean
*/
function checkCourse($course) {
// check if has loop
if(isset($this->visiting[$course])) return false ;
// check if is completed
if($this->coursePrerequisites[$course] == []) return true ;
// mark as visiting
$this->visiting[$course] = true ;
// iterate over pre requisite courses
foreach($this->coursePrerequisites[$course] as $preCourse){
if(!$this->checkCourse($preCourse)) return false ;
}
// unmark as visiting
unset($this->visiting[$course]);
// if get to the end, so we can clean the pre requisites , and it means that course can be completed
$this->coursePrerequisites[$course] = [];
return true ;
}
}