Short Problem Definition:
There are N integers in an array A. All but one integer occur in pairs. Your task is to find out the number that occurs only once.
Link
Complexity:
time complexity is O(N);
space complexity is O(1)
Execution:
XORing two equal numbers cancels them out. XOR all numbers together.
Solution:
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#!/usr/bin/py def lonelyinteger(a): answer = 0 for candidate in a: answer ^ = candidate return answer if __name__ = = '__main__' : a = input () b = map ( int , raw_input ().strip().split( " " )) print lonelyinteger(b) 