data structures - Complexity of the algorithm that represnts the expression (n*(n-1)/2) -

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for equation : (n(n-1))/2

if write algorithm represent equation, complexity of such algorithm?

(n*(n-1))/2 can represented (1 + 2 + ... + (n-1)). finding sum using expanded expression have o(n) time complexity , o(1) space complexity.

if don't expand (n*(n-1))/2 sum-expression, takes o(1) time complexity (n*(n-1))/2.

why o(n) expanded(sum) expression?

since going addition considering (n-1) elements 1 one. o(n) considered same o(n-1).


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