Python

Solution

def getMax(operations):

stack = list()
sol = list()
max_number = [0]

for i in operations:
    if i[0]=='1':
        number = int(i[2:])
        stack.append(number)
        if number >= max_number[-1]:
            max_number.append(number)

    elif i[0]=='2' and stack:
        poppednumber = stack.pop()
        if poppednumber==max_number[-1]:
            max_number.pop()

    elif i[0]=='3':
        sol.append(max_number[-1])

return sol