Answers for "Function to find a duplicate element in a limited range list"

Function to find a duplicate element in a limited range list

def findDuplicate(A):
 
    xor = 0
 
    # take xor of all list elements
    for i in range(len(A)):
        xor ^= A[i]
 
    # take xor of numbers from 1 to `n-1`
    for i in range(1, len(A)):
        xor ^= i
 
    # same elements will cancel each other as a ^ a = 0,
    # 0 ^ 0 = 0 and a ^ 0 = a
 
    # `xor` will contain the missing number
    return xor