Get the Middle Character

You are going to be given a word. Your job is to return the middle character of the word. If the word's length is odd, return the middle character. If the word's length is even, return the middle 2 characters.

#Examples:

Kata.getMiddle("test") should return "es"

Kata.getMiddle("testing") should return "t"

Kata.getMiddle("middle") should return "dd"

Kata.getMiddle("A") should return "A"

#Input

A word (string) of length 0 < str < 1000 (In javascript you may get slightly more than 1000 in some test cases due to an error in the test cases). You do not need to test for this. This is only here to tell you that you do not need to worry about your solution timing out.

#Output

The middle character(s) of the word represented as a string.

自己的编译都无法通过的垃圾代码

section .text
global get_middle
extern strlen
extern malloc
; void get_middle(const char *s, char *buf)
; Write the result to `buf`. Don't forget to add a null byte.
get_middle:
  call strlen
  mov rcx,rax
  
  cmp rcx,0
  je .st2
  
  mov rsi,rdi
  and rcx,1
  
  cmp rcx,1
  je .st1
  
  
  mov rcx,rax
  shr rcx,2
  mov rdi,3
  call malloc
  mov byte [rdi],byte [rsi+rcx-1]
  mov byte [rdi+1],byte [rsi+rcx]
  mov byte[rdi+2],0
  mov buf,rdi
  jmp .st2
  .st1:
  mov rcx,rax
  shr rcx,2
  mov rdi,2
  call malloc
  mov byte[rdi],byte[rsi+rcx]
  mov byte[rdi+1],0
  mov buf,rdi
  
  .st2:
  ret

大神的代码

section .text
global get_middle
; void get_middle(const char *s, char *buf)
; Write the result to `buf`. Don't forget to add a null byte.
get_middle:
  xor rcx, rcx
  dec rcx ; rcx = 0xFFFFFFFFFFFFFFFF
  xor rax, rax ; rax = \0
  mov [rsi], rax ; buf = {0, 0, 0,}
  push rdi
  cld
  repne scasb
  pop rdi ; rdi = s
  neg rcx
  sub rcx, 2 ; rcx = strlen(s)
  mov rax, rcx
  xor rdx, rdx ; rdx:rax = strlen(s)
  mov rbx, 2
  div rbx ; rax = strlen(s) / 2
  mov bl, [rdi + rax] ; rbx = center or right symbol
  test rcx, 1
  jnz return ; if (rcx & 1 == 0) even
  mov [rsi + 1], bl
  mov bl, [rdi + rax - 1] ; rbx = left symbol
return:
  mov [rsi], bl
  ret

第二个

extern strlen

section .text
global get_middle
; void get_middle(const char *s, char *buf)
get_middle:
                push    rdi
                push    rsi
                push    rbp
                call    strlen
                pop     rbp
                pop     rsi
                pop     rdi
                dec     rax
                shr     rax, 1
                sbb     ecx, ecx
                mov     dl, [rdi + rax]
                mov     [rsi], dl
                and     cl, [rdi + rax + 1]
                mov     [rsi + 1], cl
                mov     [rsi + 2], byte 0                
                ret

第三个

section .text
global get_middle
; void get_middle(const char *s, char *buf)
; Write the result to `buf`. Don't forget to add a null byte.
get_middle:
  call get_length
  mov rcx, 2
  cqo ;zero rdx for division instruction
  idiv rcx
  add rdi, rax;move to the halfway point
  add rdi, rdx;if it's odd, moves to the ACTUAL halfway point
  dec rdi; 0 index
  mov al, BYTE [rdi]
  mov BYTE [rsi], al;get our first character
  test rdx, rdx
  jnz finish
  inc rsi
  mov al, BYTE [rdi+1]
  mov BYTE [rsi], al;get the second character
  finish:
    mov BYTE [rsi+1], 0
  ret
get_length:
  push rdi
  xor rax, rax
  bg_loop:
    xor rbx, rbx
    cmp BYTE [rdi], 0
    setne bl
    movzx rbx, bl
    add rax, rbx
    inc rdi
    test rbx, rbx
    jnz bg_loop
  pop rdi
  ret

 第四个

section .text
global get_middle
get_middle:
  xor   rax,rax
  mov   rcx,-1
  repne scasb
  dec   rcx
  sar   rcx,1
  mov   ax,[rdi+rcx]
  mov   [rsi],ax
  adc   rsi,1
  mov   byte[rsi],0
  ret

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