Big O Notation for space complexity of converting a string to char array

问题

Given a string String str= "absdf"; of N length and if we convert the same string to char Array using - char [] arr=str.toCharArray();.

Is it consider to be an extra space of O(N) or it will be O(1)?

回答1:

It is O(N) as suggested by @andy, the implementation of String.toCharArray() is something like:

public char[] toCharArray() {
  char result[] = new char[value.length];
  // copy the contents
  return result;
}

回答2:

Time Complexity will be O(N). Similar to creating a new Array equal to the length of the String and copying the String to the Character Array. Creating an array takes O(N) time and copying takes O(N). So total worst case complexity will be O(N).

回答3:

Its O(N)

public char[] toCharArray() {
    // Cannot use Arrays.copyOf because of class initialization order issues
    char result[] = new char[value.length];
    System.arraycopy(value, 0, result, 0, value.length);
    return result;
}

This code is taken from openjdk implementation. We are trying to iterate each element of string and copy it into the each cell of array. Number of iteration will be length of string.

来源：https://stackoverflow.com/questions/61127378/big-o-notation-for-space-complexity-of-converting-a-string-to-char-array