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Floyd's algorithm for SICP exercise 3.19
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| (define (has-cycle? ls) | |
| (define (has-cycle-h tortoise hare) | |
| (cond ((null? hare) #f) | |
| ((null? (cdr hare)) #f) | |
| ((eq? (car tortoise) (car hare)) #t) | |
| (else | |
| (has-cycle-h (cdr tortoise) (cddr hare))))) | |
| (cond ((null? ls) #f) | |
| (else (has-cycle-h ls (cdr ls))))) |
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Purty. Note the complete absence of
set!.(Courtesy of http://en.literateprograms.org/Floyd's_cycle-finding_algorithm_(Scheme))