我如何使用它们的和对一列坐标（x，y）排序

Question

如何在Racket / Scheme博士中使用它们的总和对坐标（x，y）列表进行排序

(sort-points (list (list 2 1) (list 0 0)
(list 0 3) (list -2 4))
=> (list (list 0 0) (list -2 4) (list 0 3) (list 2 1))

Answer 1

您可以将比较器传递到sort中，告诉它如何对列表中的元素进行排序。

sort

编辑1：不包含lambda：

#lang racket

(sort (list (list 2 1) (list 0 0) (list 0 3) (list -2 4))
      (λ (x y) ; less-than?
        (<= (+ (first x) (second x))
            (+ (first y) (second y)))))
; => '((0 0) (-2 4) (0 3) (2 1))

Edit 2：通过修改您在

#lang racket 

(define (my-sort l)
  (define (cmp x y)
    (<= (+ (first x) (second x))
        (+ (first y) (second y))))
  (sort l cmp))

(my-sort (list (list 2 1) (list 0 0) (list 0 3) (list -2 4)))
; => '((0 0) (-2 4) (0 3) (2 1))

注释中提供的代码：

this