Exclusive Time of Functions

Given the running logs of n functions that are executed in a nonpreemptive single threaded CPU, find the exclusive time of these functions.

Each function has a unique id, start from 0 to n-1. A function may be called recursively or by another function.

A log is a string has this format : function_id:start_or_end:timestamp. For example, "0:start:0" means function 0 starts from the very beginning of time 0. "0:end:0" means function 0 ends to the very end of time 0.

Exclusive time of a function is defined as the time spent within this function, the time spent by calling other functions should not be considered as this function's exclusive time. You should return the exclusive time of each function sorted by their function id.

Example 1: Input: n = 2 logs = ["0:start:0", "1:start:2", "1:end:5", "0:end:6"] Output:[3, 4]

Explanation: Function 0 starts at time 0, then it executes 2 units of time and reaches the end of time 1. Now function 0 calls function 1, function 1 starts at time 2, executes 4 units of time and end at time 5. Function 0 is running again at time 6, and also end at the time 6, thus executes 1 unit of time. So function 0 totally execute 2 + 1 = 3 units of time, and function 1 totally execute 4 units of time.

Solution: Using stack

• We need stack to save function call, we just need to store the id and timestamp
• We also create a vector of size n to store the exclusive time of each function
• Iterate through the logs, extract the id, start or end, timestamp
• If it's the start of a function, we update the current function's exclusive time if there's any, then push the new function
• If it's the end of a function, we update the current function's exclusive time, then update the previous function's timestamp if there's any.

vector<int> exclusiveTime(int n, vector<string>& logs) {
    // 1. We need stack to save function call stack<pair<int, int>>, key and latest start time
    // 2. We need vector to store the exclusive time

    vector<int> time(n, 0);
    stack<pair<int, int>> s;
    for (auto log: logs) {
        auto pos = log.find(":");
        int id = atoi(log.substr(0, pos).c_str());
        log = log.substr(pos+1);

        pos = log.find(":");
        string startOrEnd = log.substr(0, pos);
        log = log.substr(pos+1);

        int timestamp = stoi(log);
        if (startOrEnd == "start") {
            // 3. Update the exclusive time in previous function
            if (!s.empty()) time[s.top().first] += timestamp - s.top().second;
            s.push({id, timestamp});
        } else {
            // 4. Update the current function's exclusive time
            time[id] += timestamp - s.top().second + 1;
            s.pop();

            // 5. Update the caller function
            if (!s.empty()) s.top().second = timestamp + 1;
        }
    }

    return time;
}