How to achieve string flipping? If PHP built-in functions are not allowed, please use programming to achieve it?

In programming, string flipping is a very common problem. Most programming languages ​​have built-in string flipping functions. However, if built-in functions are not allowed, how can we achieve string flipping?

This article will introduce several different methods and programming techniques for implementing string flipping. These methods work with most programming languages, including PHP.

Method 1: Loop iteration

This is the most common string flipping method. The method is very simple, just start traversing from the last character of the string and splice the characters into a new string one by one.

We can use the following PHP code to implement this method:

function reverse_string($str) {
  $new_str = "";
  $len = strlen($str);
  for ($i = $len - 1; $i >= 0; $i--) {
    $new_str .= $str[$i];
  }
  return $new_str;
}

Using this method, if you want to flip the string "Hello World!", "!dlroW olleH" will be output.

Method 2: Recursion

Recursion is a very useful programming technique. To implement the recursive method of string flipping, we need to split the string into two parts: the first character and the remaining characters. We can put the first character last and call the function recursively to process the remaining characters.

The following PHP code implements this method:

function reverse_string($str) {
  if (strlen($str) == 0) {
    return $str;
  } else {
    return reverse_string(substr($str, 1)) . $str[0];
  }
}

Using this method, if you want to flip the string "Hello World!", you will output "!dlroW olleH".

Method Three: Using the Stack

If you are familiar with data structures, you may have thought of this method. String flipping is very convenient using the stack. We use a stack to store all the characters in the string, then pop each character from the stack and concatenate them together to get the reverse string.

The following PHP code implements this method:

function reverse_string($str) {
  $stack = new SplStack();
  $len = strlen($str);
  for ($i = 0; $i < $len; $i++) {
    $stack->push($str[$i]);
  }
  $new_str = "";
  while (!$stack->isEmpty()) {
    $new_str .= $stack->pop();
  }
  return $new_str;
}

Using this method, if you want to flip the string "Hello World!", you will output "!dlroW olleH".

Summary

There are many ways to implement string flipping. This article introduces three common methods: loop iteration, recursion and using the stack. These methods are based on programming techniques rather than built-in functions, so they can be used in any programming language.

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