后台开发 3个题目 array_chunk, 100块钱找零钱(动态规划 dynamic programming), 双向循环链表 llist 删除节点

1. array_chunk 实现

   http://php.net/manual/en/function.array-chunk.php

<?php
function my_array_chunk($a, $sz) {
	$b = [];
	if ($sz < 1) {
        throw new Exception("size is less than 1");
		return null;
	}
	for ($i = 0, $n = count($a); $i < $n; $i++) {
		if ($i % $sz === 0) {
			array_push($b, []);
		}
		array_push($b[count($b) - 1], $a[$i]);
	}
	return $b;
}

　　

　　test:

$input_array = array('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h');
print_r(my_array_chunk($input_array, 3));
// print_r(my_array_chunk($input_array, 2));

 

　　output:　

E:\code\php>php chunk.php
Array
(
    [0] => Array
        (
            [0] => a
            [1] => b
            [2] => c
        )

    [1] => Array
        (
            [0] => d
            [1] => e
            [2] => f
        )

    [2] => Array
        (
            [0] => g
            [1] => h
        )

)

 

  javascript:

Array.prototype.chunk = function(sz) {
    var a = [];
    if (sz<1) {
       	throw new Error("size is less than 1");
    }
    this.forEach(function(e, i) {
        if (i % sz === 0) {
            a.push([]);
        }
        a[a.length-1].push(e);         
    });
    return a;
};

　　

　　test:

var a = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'];
console.log(a.chunk(2));
console.log(a.chunk(1));
console.log(a.chunk(8));
console.log(a.chunk(10));
console.log(a.chunk(0));

　　output:

E:\code\js\algorithm>node array_chunk.js
[ [ 'a', 'b' ], [ 'c', 'd' ], [ 'e', 'f' ], [ 'g', 'h' ] ]
[ [ 'a' ],
  [ 'b' ],
  [ 'c' ],
  [ 'd' ],
  [ 'e' ],
  [ 'f' ],
  [ 'g' ],
  [ 'h' ] ]
[ [ 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h' ] ]
[ [ 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h' ] ]
[ 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h' ]

 

* golang

// HelloWorld project main.go

package main

import (
	"fmt"
)

func array_chunk(a []string, sz int) [][]string {
	var n int = len(a)/sz   // 二维数组的长度
    if (len(a)>n*sz) { n += 1 }
	var b = make([][]string, 0, n)

	for i := 0; i < len(a); i++ {
		offset := i % sz
		if offset == 0 {
			b = append(b, make([]string, sz))
		}
		b[len(b)-1][offset] = a[i]
	}
	return b
}

func slice2d_toString(a [][]string) string {
	s := "["

	for i := 0; i < len(a); i++ {
		s += "["
		j := 0
		for ; j < len(a[i])-1; j++ {
			s += a[i][j] + ","
		}
		s += a[i][j] + "] "
	}

	s += "]"
	return s
}

func main() {
	letters := []string{"a", "b", "c", "d", "e", "f", "g"}
	a2d := array_chunk(letters, 3)
	fmt.Printf(slice2d_toString(a2d))
}

　　output:

C:/go/bin/go.exe build -i [J:/gocode/src/HelloWorld]
成功: 进程退出代码 0.
J:/gocode/src/HelloWorld/HelloWorld.exe  [J:/gocode/src/HelloWorld]
[[a,b,c] [d,e,f] [g,,] ]成功: 进程退出代码 0.

Java:

package cn.mediamix;

import java.util.ArrayList;

public class ArrayChunk {
	
	private static ArrayList<ArrayList<String>> arrayChunk(String[] input, int sz) 
			throws Exception {
		ArrayList<ArrayList<String>> a = new ArrayList<ArrayList<String>>();
		if (sz < 1) {
			throw new Exception("size is less than 1");
		}
		for (int i = 0, n = input.length; i < n; i++) {
			if (i % sz == 0) {
				a.add(new ArrayList<String>());
			}
			a.get(a.size()-1).add(input[i]);
		}
		
		return a;
	}

	public static void main(String[] args) {
		String[] input = {"a", "b", "c", "d", "e", "f", "g", "h"};
		ArrayList<ArrayList<String>> a = null;
		try {
			a = arrayChunk(input, 3);
		} catch (Exception e) {
			e.printStackTrace();
		}
		System.out.println(a.toString());
	}
}

　　Output: 

[[a, b, c], [d, e, f], [g, h]]

 

2. 100块钱 找零钱多少种方法  50, 20, 10, 5, 1

   查一下贪心算法、0/1背包问题  (343种, 但是套4层循环不是好的方法)

  先看一个简单一点的问题: 93块钱找零钱，用最少的note/coins数怎么做?

function findMin(deno, v) {
    deno = deno.sort(function(a, b) {
       return b-a;
    });
    var ans = [];
    deno.forEach(function(item) {
        while (v >= item) {
            v -= item;
            ans.push(item);
        }
    });
    return ans;
}

var deno = [50, 20, 10, 5, 1];
console.log(findMin(deno, 93));

　　output: 

[ 50, 20, 20, 1, 1, 1 ]

 

100块钱, 用面值 [ 50, 20, 10, 5, 1 ]的钱币, 换零钱多少种方法?

用动态规划法:

php:

<?php
function coins($deno, $v) {
    $n = count($deno);
    $dp = [];
    for ($i = 0; $i < $n; $i++) {
        $dp[$i] = [];  // length: $v+1
        $dp[$i][0] = 1; //第一列为1
    }
    for ($j = 0; $j <= $v; $j++) {
        // 第一行中能够被$deno[0]整除的数，即可以被换钱，记为1
        $dp[0][$j] = $j % $deno[0]===0 ? 1 : 0;
    }
    for ($i = 1; $i < $n; $i++) {
        for ($j = 1; $j <= $v; $j++) {
            $tmp = 0;
            for ($k = 0; $k * $deno[$i] <= $j; $k++) {
                // 累加用$k张$deno[i]货币后$dp[i-1]中组成剩下钱数的方法数
                $tmp += $dp[$i-1][ $j - $k * $deno[$i] ];
            }
            $dp[$i][$j] = $tmp;
        }
    }
    return $dp[$n-1][$v];
}

// test
$deno = [50,20,10,5,1];
echo coins($deno, 100).PHP_EOL;

　　

javascript:

function coins(deno, v) {
    if (deno === null || deno.length === 0 || v < 0) {
        return 0;
    }
    var dp = new Array(v + 1);
    // init
    for (var i = 0; i < dp.length; i++) {
        dp[i] = 0;
    }
    for (var j = 0; deno[0] * j <= v; j++) {
        dp[deno[0] * j] = 1;
    }
    for (i = 1; i < deno.length; i++) {
        for (j = 1; j <= v; j++) {
            dp[j] += j - deno[i] >= 0 ? dp[j - deno[i]] : 0;
        }
    }
    return dp[v];
}

　　

// test
var deno = [50, 20, 10, 5, 1];
console.log(coins(deno, 100));  // 343

golang: 

// Dynamic programming project main.go
package main

import (
	"fmt"
)

func coin(deno []int, v int) int {
	n := len(deno)
	dp := make([][]int, 0, n)
	for i := 0; i < n; i++ {
		dp = append(dp, make([]int, v+1))
		dp[i][0] = 1
	}
	for j := 0; j <= v; j++ {
		if j%deno[0] == 0 {
			dp[0][j] = 1
		} else {
			dp[0][j] = 0
		}
	}
	for i := 1; i < n; i++ {
		for j := 1; j <= v; j++ {
			tmp := 0
			for k := 0; k*deno[i] <= j; k++ {
				tmp += dp[i-1][j-k*deno[i]]
			}
			dp[i][j] = tmp
		}
	}
	return dp[n-1][v]
}

func main() {
	deno := make([]int, 0, 5)
	deno = append(deno, 50, 20, 10, 5, 1)

	/*
		for i := range deno {
			fmt.Println(deno[i])
		}
	*/
	c := coin(deno, 100)
	fmt.Println(c)
}

　　output:

/usr/local/go/bin/go build -i [/Users/Mch/Code/golang/src/Greedy]
Success: process exited with code 0.
/Users/Mch/Code/golang/src/Greedy/Greedy  [/Users/Mch/Code/golang/src/Greedy]
343
Success: process exited with code 0.

Java:

package cn.mediamix;

public class Coins {
	
	public static int coins(int []deno, int v) {
		if (deno == null || deno.length == 0 || v < 0) {
			return 0;
		}
		int[] dp = new int[v+1];
		for (int j = 0; deno[0] * j <= v; j++) {
			dp[deno[0]*j] = 1;
		}
		for (int i = 1; i < deno.length; i++) {
			for (int j = 1; j <= v; j++) {
				dp[j] += j - deno[i] >= 0 ? dp[j-deno[i]] : 0;
			}
		}
		return dp[v];
	}

	public static void main(String[] args) {
		int []deno = {50, 20, 10, 5, 1};
		int solutions = Coins.coins(deno, 100);
		System.out.println(solutions);
	}

}

　　output:  343 

 

3. 双向链表删除节点 (只有1个节点怎么处理)

   为了让链表的元素适应任何类型, 参照内核链表. http://kernel.org

    ~/linux-4.17.11/include/linux/list.h

    ~/linux-4.17.11/include/linux/kernel.h

    ~/linux-4.17.11/include/linux/stddef.h

    ~/linux-4.17.11/include/linux/poison.h

　　llist.h

#ifndef llist_h
#define llist_h

struct list_head {
    struct list_head *next;
    struct list_head *prev;
};

// #define offsetof(TYPE, MEMBER) ((size_t)&((TYPE *)0)->MEMBER)

#define list_entry(ptr, type, member)  \
container_of(ptr, type, member)

#define container_of(ptr, type, member) ({ \
void *__mptr = (void *)(ptr);   \
((type *)(__mptr - offsetof(type, member))); })

#define LIST_HEAD_INIT(name) { &(name), &(name) }

#define LIST_HEAD(name) \
struct list_head name = LIST_HEAD_INIT(name)

static inline void INIT_LIST_HEAD(struct list_head *list)
{
    list->next = list;
    list->prev = list;
}

static inline void __list_add(struct list_head *new,
                              struct list_head *prev,
                              struct list_head *next)
{
    next->prev = new;
    new->next = next;
    new->prev = prev;
    prev->next = new;
}

static inline void list_add_tail(struct list_head *new, struct list_head *head)
{
    __list_add(new, head->prev, head);
}

static inline void list_add(struct list_head *new, struct list_head *head)
{
    __list_add(new, head, head->next);
}

static inline void __list_del(struct list_head * prev, struct list_head * next)
{
    next->prev = prev;
    prev->next = next;
}

static inline void __list_del_entry(struct list_head *entry)
{
    // if (!__list_del_entry_valid(entry)) return;
    __list_del(entry->prev, entry->next);
}

#define POISON_POINTER_DELTA 0

#define LIST_POISON1  ((void *) 0x100 + POISON_POINTER_DELTA)
#define LIST_POISON2  ((void *) 0x200 + POISON_POINTER_DELTA)

static inline void list_del(struct list_head *entry)
{
    __list_del_entry(entry);
    entry->next = LIST_POISON1;
    entry->prev = LIST_POISON2;
}

　　

main.c

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include "llist.h"

struct fox {
    unsigned long tail_length;
    unsigned long weight;
    bool is_fantastic;
    struct list_head list;
};

void handler(struct fox *f) {
    printf("tail length: %lu, weight=%lu, fantasic: %d\n",
           f->tail_length, f->weight, f->is_fantastic?1:0);
}

struct fox *list_traverse(const struct list_head *fox_list,
                          void (*handler)(struct fox *f)) {
    // 链表指针(不包含元素)迭代器
    struct list_head *p;
    // 链表整个节点迭代器
    struct fox *f = NULL;
    
    list_for_each(p, fox_list) {
        f = list_entry(p, struct fox, list);
        handler(f);
    }
    return f;
}

int main(int argc, const char * argv[]) {
    /*
    struct fox *red_fox = (struct fox *)malloc(sizeof(*red_fox));    
    red_fox->tail_length = 40;
    red_fox->weight = 6;
    red_fox->is_fantastic = false;
    INIT_LIST_HEAD(&red_fox->list);
    */
    struct fox red_fox = {
        .tail_length = 40,
        .weight = 6,
        .is_fantastic = false,
        .list = LIST_HEAD_INIT(red_fox.list)
    };
    
    struct fox new_fox = {
        .tail_length = 35,
        .weight = 5,
        .is_fantastic = true,
        .list = LIST_HEAD_INIT(new_fox.list)
    };
    // 初始化表头
    LIST_HEAD(fox_list);
    // 添加2个节点
    list_add_tail(&red_fox.list, &fox_list);
    list_add_tail(&new_fox.list, &fox_list);
    
    struct fox *f = list_traverse(&fox_list, handler);
    
    // 删除最后添加的一个节点
    list_del(&f->list);
    printf("after deleted\n");
    f = list_traverse(&fox_list, handler);
    
    // 同理再删除一个节点
    list_del(&f->list);
    printf("after deleted\n");
    list_traverse(&fox_list, handler);
    
    return 0;
}

　　output:

tail length: 40, weight=6, fantasic: 0

tail length: 35, weight=5, fantasic: 1

after deleted

tail length: 40, weight=6, fantasic: 0

after deleted

Program ended with exit code: 0