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Exclusive Time of Functions

Problem Statement​

On a single-threaded CPU, we execute a program containing n functions. Each function has a unique ID between 0 and n-1.

Function calls are stored in a call stack: when a function call starts, its ID is pushed onto the stack, and when a function call ends, its ID is popped off the stack. The function whose ID is at the top of the stack is the current function being executed. Each time a function starts or ends, we write a log with the ID, whether it started or ended, and the timestamp.

You are given a list logs, where logs[i] represents the ith log message formatted as a string "{function_id}:{"start" | "end"}:{timestamp}". For example, "0:start:3" means a function call with function ID 0 started at the beginning of timestamp 3, and "1:end:2" means a function call with function ID 1 ended at the end of timestamp 2. Note that a function can be called multiple times, possibly recursively.

A function's exclusive time is the sum of execution times for all function calls in the program. For example, if a function is called twice, one call executing for 2 time units and another call executing for 1 time unit, the exclusive time is 2 + 1 = 3.

Return the exclusive time of each function in an array, where the value at the ith index represents the exclusive time for the function with ID i.

Leetcode Link

Code​

Python
def exclusiveTime(self, N, logs):
    ans = [0] * N
    stack = []
    prev_time = 0

    for log in logs:
        fn, typ, time = log.split(':')
        fn, time = int(fn), int(time)

        if typ == 'start':
            if stack:
                ans[stack[-1]] += time - prev_time
            stack.append(fn)
            prev_time = time
        else:
            ans[stack.pop()] += time - prev_time + 1
            prev_time = time + 1

    return ans