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> **Possible Duplicate:**  
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> [Plain English explanation of Big O](https://stackoverflow.com/questions/487258/plain-english-explanation-of-big-o) 
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Many times when time complexity of a algorithm is talked about, memory also comes into account. I want to know what is the meaning of big-O(1), big-O(n), big-O(n\*n) memory?

And how it is related to time complexity?