问题
I'm working on sorting a list of lists by their first element for example
(sort (list '(2 1 6 7) '(4 3 1 2 4 5) '(1 1))))
expected output => ('(1 1) '(2 1 6 7) '(4 3 1 2 4 5))
The algorithm I used is bubble sort. And I modified it to deal with lists. However, the code doesn't compile. The error is
mcar: contract violation
expected: mpair?
given: 4
Can someone correct my code and explain it. Thank you
(define (bubble L)
(if (null? (cdr L))
L
(if (< (car (car L)) (car (cadr L)))
(list (car L)
(bubble (car (cdr L))))
(list (cadr L)
(bubble (cons (car (car L)) (car (cddr L))))))))
(define (bubble-sort N L)
(cond ((= N 1) (bubble L))
(else
(bubble-sort (- N 1) (bubble L)))))
(define (bubble-set-up L)
(bubble-sort (length L) L))
(define t3 (list '(2 1 6 7) '(4 3 1 2 4 5) '(1 2 3) '(1 1)))
(bubble-set-up t3)
回答1:
I have fixed a few mistakes. There is at least one mistake left.
Consider the case where L
only contains one element.
#lang r5rs
(define (bubble L)
(if (null? (cdr L))
L
(if (< (car (car L)) (car (cadr L)))
(cons (car L)
(bubble (cdr L)))
(cons (cadr L)
(bubble (cons (car L) (cddr L)))))))
(define (bubble-sort N L)
(cond ((= N 1) (bubble L))
(else
(bubble-sort (- N 1) (bubble L)))))
(define (bubble-set-up L)
(bubble-sort (length L) L))
(define t3 (list '(2 1 6 7) '(4 3 1 2 4 5) '(1 2 3) '(1 1)))
(display (bubble-set-up t3))
(newline)
回答2:
How about (sort (lambda (x y)(< (car x)(car y))) <YOUR_LIST>)
?
来源:https://stackoverflow.com/questions/40056854/sorting-list-of-lists-by-their-first-element-in-scheme