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
