# CSPT17 Lecture 4 - Memory Basics
## [ToLowerCase](https://leetcode.com/problems/to-lower-case/)

class Solution:
    """
    Understand
    
    "HELLO" --> "hello"
    "hElLo" --> "hello"
    "hEllo1" --> "hel lo1"
    
    Plan
    Hint 1: all upper-case letters encoding have value > 64 AND < 91
    Hint 2: the lower-case equivalent of an upper-case character is it's encoding +32
    Hint 3: you can use ord(x) to get the encoding value of a character. You can use chr(x) to convert back to a character.
    
    create a new string
    go through each character in the original string
    if character is an upper-case character, the lower-case character is + 32
    return the new string that we just created
    
    Runtime: O(n)
    Space: O(n)
    """
    def toLowerCase(self, str: str) -> str:
        encodedChars = [ord(x) for x in str]
        for i in range(len(encodedChars)):
            if encodedChars[i] > 64 and encodedChars[i] < 91:
                encodedChars[i] += 32
        decodedChars = [chr(x) for x in encodedChars]
        return ''.join(decodedChars)

## [Hamming Weight](https://leetcode.com/problems/number-of-1-bits/)

class Solution:
    """
    Hint: You can use bin(n) to get the string representation of
    the binary equivalent for a number
    
    Understand
    0 -> 0
    1 -> 1
    2 "10"-> 1
    
    Plan
    Convert number to string, then walk through string and count 1s
    
    Runtime: O(1)
    Space: O(1)
    """
    def hammingWeight(self, n: int) -> int:
        return bin(n).count('1')