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# The “Big O Notation” In Simple Terms.

## 4 Common “O” Notations:

`T = N = c * 1 = O(1)`
`X = ['A', 'B', 'C', 'D']X[3] = D`
`print("Please select from the following items:")print("1 - Potato Chips")print("2 - Pretzels")print("3 - Nachos")print("4 - Popcorn")optNum = input("Type number: ")var = int(optNum)if var == 1:   print("You have chosen Potato Chips")   print(var)elif var == 2:   print("You have chosen Pretzels")   print(var)elif var == 3:   print("You have chosen Nachos")   print(var)elif var == 4:   print("You have chosen Popcorn")   print(var)else:   print("Invalid Option, try again")   print(var)print("Good bye!")`
`T = aN + B = N = O(N)`
`X = ['A', 'B', 'D', 'E', 'F']X.insert(2, 'C')X = ['A', 'B', 'C', 'D', 'E', 'F']`
`Y = ['apple', 'banana', 'mango', 'grapes', 'pineapple', 'durian']`
`def search(Y, n, x):for i in range (0, n): if (Y[i] == x):    return i;    return -1;Y = [‘apple’, ‘banana’, ‘mango’, ‘grapes’, ‘pineapple’, ‘durian’]x = “pineapple”;n = len(Y);result = search(Y, n, x)if(result == -1): print(“Element is not present in the list”)else: print(“Element”, x, “is present at index”, result)`
`T = n*(n+1)/2 = n² + n/2 = O(N²)`
`X = [21, 5, 3, 18, 30, 2, 8] -> X = [2, 3, 5, 8, 18, 21, 30]`
`X = [21, 5, 3, 18, 30, 2, 8]def bubbleSort(X):    n = len(X)    for i in range(n):            for j in range(0, n-i-1):            if X[j] > X[j+1] :                X[j], X[j+1] = X[j+1], X[j]bubbleSort(X)print("This is the sorted list: ")for i in range(len(X)):    print("%d" %X[i])`
`X.sort()[2, 3, 5, 8, 18, 21, 30]`
`T = Log N² = O(Log N)`
`X = [10, 15, 35, 42, 60, 70, 82, 94]`
`def binary_search(X, item):    first = 0    last = len(X)-1    found = False    while( first<=last and not found):        mid = (first + last)//2        if X[mid] == item :            found = True            print(“The element item”, item, “was found at index “,   X.index(60))        else:            if item < X[mid]:                last = mid — 1            else:                first = mid + 1   return foundprint(binary_search([10, 15, 35, 42, 60, 70, 82, 94], 60))`

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