Add Shortest Remaining Time First (SRTF) scheduling algorithm

Author: Upanishadkachroo

scheduling/shortest_remaining_time_first.py

@@ -0,0 +1,98 @@
+"""
+Shortest Remaining Time First (SRTF) Scheduling Algorithm.
+SRTF is the preemptive version of Shortest Job First (SJF).
+At every moment, the process with the smallest remaining burst time is executed.
+https://en.wikipedia.org/wiki/Shortest_remaining_time
+"""
+
+from __future__ import annotations
+from statistics import mean
+
+
+def calculate_waiting_times(burst_times: list[int], arrival_times: list[int]) -> list[int]:
+    """
+    Calculate the waiting times of processes using SRTF scheduling.
+
+    Args:
+        burst_times: List of burst times for each process.
+        arrival_times: List of arrival times for each process.
+
+    Returns:
+        A list containing waiting time for each process.
+
+    Examples:
+    >>> calculate_waiting_times([6, 8, 7, 3], [0, 1, 2, 3])
+    [9, 15, 10, 0]
+    >>> calculate_waiting_times([5, 4, 2, 1], [0, 1, 2, 3])
+    [6, 3, 1, 0]
+    """
+    n = len(burst_times)
+    remaining_times = burst_times.copy()
+    waiting_times = [0] * n
+    complete = 0
+    t = 0
+    min_remaining = float("inf")
+    shortest = 0
+    check = False
+    finish_time = 0
+
+    while complete != n:
+        # Find process with minimum remaining time at current time
+        for j in range(n):
+            if arrival_times[j] <= t and remaining_times[j] < min_remaining and remaining_times[j] > 0:
+                min_remaining = remaining_times[j]
+                shortest = j
+                check = True
+
+        if not check:
+            t += 1
+            continue
+
+        # Reduce remaining time of current process
+        remaining_times[shortest] -= 1
+        min_remaining = remaining_times[shortest]
+        if min_remaining == 0:
+            min_remaining = float("inf")
+
+        # If a process finishes
+        if remaining_times[shortest] == 0:
+            complete += 1
+            check = False
+            finish_time = t + 1
+            waiting_times[shortest] = (
+                finish_time - burst_times[shortest] - arrival_times[shortest]
+            )
+            if waiting_times[shortest] < 0:
+                waiting_times[shortest] = 0
+
+        t += 1
+
+    return waiting_times
+
+
+def calculate_turn_around_times(
+    burst_times: list[int], waiting_times: list[int]
+) -> list[int]:
+    """
+    Calculate turn-around times for each process.
+
+    >>> calculate_turn_around_times([6, 8, 7, 3], [9, 15, 10, 0])
+    [15, 23, 17, 3]
+    """
+    return [burst + waiting for burst, waiting in zip(burst_times, waiting_times)]
+
+
+if __name__ == "__main__":
+    burst_times = [6, 8, 7, 3]
+    arrival_times = [0, 1, 2, 3]
+    waiting_times = calculate_waiting_times(burst_times, arrival_times)
+    turn_around_times = calculate_turn_around_times(burst_times, waiting_times)
+
+    print("Process ID \tArrival Time \tBurst Time \tWaiting Time \tTurnaround Time")
+    for i, burst_time in enumerate(burst_times):
+        print(
+            f"  {i + 1}\t\t  {arrival_times[i]}\t\t  {burst_time}\t\t  {waiting_times[i]}\t\t  {turn_around_times[i]}"
+        )
+    print(f"\nAverage waiting time = {mean(waiting_times):.5f}")
+    print(f"Average turn around time = {mean(turn_around_times):.5f}")
+