Previous string inversion topic

The previous issue of string inversion

The problem of string inversion , Can you think of a better way ？

A lot of people commented , Some people also wrote their own ideas for solving problems , Others have written their own code

There is also a very popular stack pressing solution

I believe that many people will encounter this kind of problem in the written examination , Give you a string , Let you find some rules , Or find a string , Or character case conversion .

Let's take a look first , If we use the stack to complete this code, how to write ？

The answer I posted above actually uses the idea of stack , Queue first in first out , Stack means first in and last out .

Stack ,C Language implementation

So the code above

In the form of stack , The last position comes out first .

What if my code is in stack form ？ I wrote a rough version

#include "stdio.h"
#include "string.h"
#include "stdlib.h"

char input[] = {"the sky is blue"};

// subject :

//input  the sky is blue
//output blue is sky the

void reverseWords(char* s, size_t n) {
 char *stack = (char*)malloc(n);
 memcpy(stack, s, n);
 for (int i=0; i<n; i++) {
  *(s + i) = *(stack + n -i -1); 
 }
 if (stack) {
  free(stack);
  stack = NULL;
 }
}

//eulb si yks eht

void reverseWords_by_space(char* s, int n) {

 int i = 0;
 int len = 0;
 for (i=0; i<n; i++) {
  if (s[i] == ' ') {
   reverseWords(s+i-len, len);
   len = 0;
  } else if (s[i] == '\0') {
   reverseWords(s+i-len, len);
   len = 0;   
  }else {
   ++len;
  }
 }

}

int main(void) {

 printf("%s\n", input);
 reverseWords(input,strlen(input));
 reverseWords_by_space(input,sizeof(input));
 printf("%s\n", input);
 //  Finished writing , If you have any comments you don't understand 
 return 0;

}

But I don't think it's very good , Because it uses Memory application , Embedded should know , Memory is a scarce resource for us .

So I still think the above student's writing is very awesome

Some people reply that XOR is used to exchange two variables , There are many ways to exchange variables , But sometimes I can't remember during the interview , So we will write the simplest way , But there are some common ways you can try .

#include "stdio.h"

void swap4(int *a,int *b) {
 *a = (*a + *b) - (*b = *a);
}

void swap3(int *a,int *b) {
 *a = (*a ^ *b) ^ (*b = *a);
}

void swap2(int *a,int *b) {
 *a = *a + *b;
 *b = *a - *b;
 *a = *a - *b;
}

void swap1(int *a,int *b) {
 *a = *a^*b;
 *b = *a^*b;
 *a = *a^*b;
}

int main(void) {
 int a = 3,b = 4;
 printf("a=%d,b=%d\n",a,b);
 swap1(&a,&b);
 printf("a=%d,b=%d\n",a,b);
 swap2(&a,&b);
 printf("a=%d,b=%d\n",a,b);
 swap3(&a,&b);
 printf("a=%d,b=%d\n",a,b);
 swap4(&a,&b);
 printf("a=%d,b=%d\n",a,b);
 return 0;

}

 Output 

 I want to update the code again in the evening 

#include "stdio.h"
#include "string.h"
#include "stdlib.h"
char input[] = {"the sky is blue cris 1212321 apple"};

// subject :

//input  the sky is blue
//output blue is sky the

void reverseWords(char* s, size_t n) {
 *(s+n-1) = '\0';
 printf("%s ",s);
}

int main(void) {
 int size = sizeof(input);
 printf("%s\n",input);
 for (int i=0,n=0; i<=size; i++,n++) {
  if (*(input+size-i-1) == ' ' || i == size){
   reverseWords(input+size-i, n);
   n = 0;
  }
 }
 return 0;
}

 If there is a better way , Welcome to leave a message .

 If you see a written test with a variant of this question , Also welcome to leave a message .