636. Exclusive Time of Functions

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.

 

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 the beginning of time 0, then it executes 2 for units of time and reaches the end of time 1.
Function 1 starts at the beginning of time 2, executes for 4 units of time, and ends at the end of time 5.
Function 0 resumes execution at the beginning of time 6 and executes for 1 unit of time.
So function 0 spends 2 + 1 = 3 units of total time executing, and function 1 spends 4 units of total time executing.

Example 2:

Input: n = 1, logs = ["0:start:0","0:start:2","0:end:5","0:start:6","0:end:6","0:end:7"]
Output: [8]
Explanation:
Function 0 starts at the beginning of time 0, executes for 2 units of time, and recursively calls itself.
Function 0 (recursive call) starts at the beginning of time 2 and executes for 4 units of time.
Function 0 (initial call) resumes execution then immediately calls itself again.
Function 0 (2nd recursive call) starts at the beginning of time 6 and executes for 1 unit of time.
Function 0 (initial call) resumes execution at the beginning of time 7 and executes for 1 unit of time.
So function 0 spends 2 + 4 + 1 + 1 = 8 units of total time executing.

Example 3:

Input: n = 2, logs = ["0:start:0","0:start:2","0:end:5","1:start:6","1:end:6","0:end:7"]
Output: [7,1]
Explanation:
Function 0 starts at the beginning of time 0, executes for 2 units of time, and recursively calls itself.
Function 0 (recursive call) starts at the beginning of time 2 and executes for 4 units of time.
Function 0 (initial call) resumes execution then immediately calls function 1.
Function 1 starts at the beginning of time 6, executes 1 units of time, and ends at the end of time 6.
Function 0 resumes execution at the beginning of time 6 and executes for 2 units of time.
So function 0 spends 2 + 4 + 1 = 7 units of total time executing, and function 1 spends 1 unit of total time executing.

Example 4:

Input: n = 2, logs = ["0:start:0","0:start:2","0:end:5","1:start:7","1:end:7","0:end:8"]
Output: [8,1]

Example 5:

Input: n = 1, logs = ["0:start:0","0:end:0"]
Output: [1]

 

Constraints:

  • 1 <= n <= 100
  • 1 <= logs.length <= 500
  • 0 <= function_id < n
  • 0 <= timestamp <= 109
  • No two start events will happen at the same timestamp.
  • No two end events will happen at the same timestamp.
  • Each function has an "end" log for each "start" log.

Rust Solution

struct Solution;

enum Action {
    Start,
    End,
}

impl Solution {
    fn exclusive_time(n: i32, logs: Vec<String>) -> Vec<i32> {
        let n = n as usize;
        let mut stack: Vec<usize> = vec![];
        let mut res: Vec<i32> = vec![0; n];
        let mut prev = 0;
        for log in logs {
            let mut it = log.split(':');
            let id: usize = it.next().unwrap().parse::<usize>().unwrap();
            let action: Action = if it.next().unwrap() == "start" {
                Action::Start
            } else {
                Action::End
            };
            let val: i32 = it.next().unwrap().parse::<i32>().unwrap();
            match action {
                Action::Start => {
                    if let Some(&top) = stack.last() {
                        res[top] += val - prev;
                    }
                    prev = val;
                    stack.push(id);
                }
                Action::End => {
                    if let Some(top) = stack.pop() {
                        res[top] += val + 1 - prev;
                        prev = val + 1;
                    }
                }
            }
        }
        res
    }
}

#[test]
fn test() {
    let n = 2;
    let logs = vec_string!["0:start:0", "1:start:2", "1:end:5", "0:end:6"];
    let res = vec![3, 4];
    assert_eq!(Solution::exclusive_time(n, logs), res);
}

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