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题解地址

https://leetcode.cn/problems/count-integers-with-even-digit-sum/solutions/2047123/by-yhm138_-w8co/ lc2180

代码

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//我的问题是，Go支持函数式编程吗？

func countEven(num int) int {
    a := makeRange(1, num)
    evenCount := len(filter(a, func(num int) bool {
        numStr := strconv.Itoa(num)
        digits := strings.Split(numStr, "")
        mySum:=0
        for _,ele :=range digits{
            d, _ := strconv.Atoi(ele)
            mySum=mySum+d
        }
        return mySum%2 == 0
    }))
    return evenCount
}


func filter(src []int, p func(int) bool) []int {
	dst := []int{}
	for _, s := range src {
		if p(s) {
			dst = append(dst, s)
		}
	}
	return dst
}

func makeRange(min, max int) []int {
    a := make([]int, max-min+1)
    for i := range a {
        a[i] = min + i
    }
    return a
}

//C++
class Solution {
public:
    int countEven(int num) {
        std::vector<int> range(num);
        std::iota(range.begin(), range.end(), 1);
        return std::count_if(range.begin(), range.end(), [](int x) {
            std::string str = std::to_string(x);
            return std::accumulate(str.begin(), str.end(), 0, [](int sum, char c) {
                return sum + (c - '0');
            }) % 2 == 0;
        });
    }
};

//C#
using System;
using System.Linq;

public class Solution {
    public int CountEven(int num) {
         return Enumerable.Range(1, num).Count(x => x.ToString().Select(c => c - '0').Sum() % 2 == 0);
    }
}

# ruby

# @param {Integer} num
# @return {Integer}
def count_even(num)
  (1..num).count { |x| x.to_s.chars.map(&:to_i).sum % 2 == 0 }
end

//swift

class Solution {
    func countEven(_ num: Int) -> Int {
        return (1...num).filter { x in
            x.description.map { Int(String($0))! }.reduce(0, +) % 2 == 0
        }.count
    }
}

//kotlin

class Solution {
    fun countEven(num: Int): Int {
        return (1..num).count {
            it.toString().toList().map { it.toInt() }.sum() % 2 == 0
        }
    }
}

//rust

impl Solution {
    pub fn count_even(num: i32) -> i32 {
        (1..num+1).filter(|x| x.to_string().chars().map(|c| c.to_digit(10).unwrap()).sum::<u32>() % 2 == 0)
                  .count() as i32
    }
}

//php

class Solution {

    /**
     * @param Integer $num
     * @return Integer
     */
    function countEven($num) {
        $result = array_filter(range(1, $num), function($x) {
            $sum = 0;
            foreach(str_split((string)$x) as $digit) {
                $sum += intval($digit);
            }
            return $sum % 2 == 0;
        });
        return count($result);
    }

}

//typescript

function countEven(num: number): number {
    return Array.from(Array(num).keys())
        .map(x => x + 1)
        .filter(x => x.toString()
            .split('')
            .map(Number)
            .reduce((a, b) => a + b, 0) % 2 === 0)
        .length;
}

;racket

(define/contract (count-even num)
  (-> exact-integer? exact-integer?)
    (length
        (filter (lambda (x)
                (even? (apply + (map char->integer (string->list (number->string x))))))
            (range 1 (add1 num))
        )
    )
)

//dart

class Solution {
  int countEven(int num) {
    return Iterable.generate(num, (x) => x+1)
        .where((x) => 
            x.toString().split('').map(int.parse).reduce((a,b) => a+b) % 2 == 0
        ).length;
    }
}

//java

import java.util.stream.IntStream;

public class Solution {
    public static int countEven(int num) {
        return (int) IntStream.range(1, num+1).filter(x -> 
            IntStream.range(0, String.valueOf(x).length())
                .map(y -> Character.getNumericValue(String.valueOf(x).charAt(y)))
                .sum() % 2 == 0
        ).count();
    }
}

#elixir

defmodule Solution do
  @spec count_even(num :: integer) :: integer
  def count_even(num) do
    (1..num)|> 
        Enum.count(fn x ->
             x |> Integer.to_string() |> String.graphemes() |> Enum.map(&String.to_integer/1) |> Enum.sum() |> rem(2) == 0
        end)
  end
end

//scala

object Solution {
    def countEven(num: Int): Int = {
        Range(1,num+1,1).count(x=>{
            x.toString.toList.map(_.toInt).sum%2==0
        });
    }
}

%erlang

sum_digits(N) ->
    sum_digits(N, 0).

sum_digits(0, Sum) -> Sum;
sum_digits(N, Sum) ->
    sum_digits(N div 10, Sum + N rem 10).


-spec count_even(Num :: integer()) -> integer().
count_even(Num) ->
    lists:foldl(fun(X, Acc) ->
                    Sum = sum_digits(X),
                    if Sum rem 2 == 0 ->
                        Acc + 1;
                    true ->
                        Acc
                    end
                end, 
    0,  [X || X <- lists:seq(1, Num)]).
    

思路

有些是拿适当的prompt问chatgpt写的。
有一些tips:

• chatgpt是真的强，没人比chatgpt更懂FP     :-p

• chatgpt分不清不同语言的Range/range是左闭右开还是左闭右闭。没事，人类也记不住。

• 写elixir的时候，chatgpt给出的答案中，匿名函数fn没有和end配对。你如果知道基础的elixir语法那很好改。

• 不知道也没事？直接拿你的代码附上报错直接问chatgpt。

correct the erlang code
sum_digits(N) ->
    sum_digits(N, 0).

sum_digits(0, Sum) -> Sum;
sum_digits(N, Sum) ->
    sum_digits(N div 10, Sum + N rem 10).


-spec count_even(Num :: integer()) -> integer().
count_even(Num) ->
    lists:foldl(fun(X, Acc) ->
                    if sum_digits(X) rem 2 == 0 ->
                        Acc + 1;
                    true ->
                        Acc
                    end
                end, 
    0,  [X || X <- lists:seq(1, Num)]).


    
Line 13: Char 24: call to local/imported function sum_digits/1 is illegal in guard
%   13|                     if sum_digits(X) rem 2 == 0 ->
%     |                        ^

)