The time complexity of an algorithm is the amount of time taken by the algorithm to complete the execution of function of its input length, n. The time complexity of an algorithm is denoted by using asymptotic notations. This manuscript specifically examines the efficiency of functions check_arm() and check_rand_arm(), these methodologies are used to find an Armstrong number in a vector. The efficiency of these two functions are calculated and assessed by using time complexity of functions. Further the space complexity also calculated, since both algorithm uses same space as per the input function. The endeavour of this paper is to express the better algorithm with respect to time.