Function to find the index of the beginning and end of the longest run in a list

Question

I\'m trying to write code that finds the longest run in a list of Boolean values and return the index of the first and last value of that run. For example, if L is [False, Fals

Answer 1

A more faster iterative version with itertools.groupby feature:

from itertools import groupby

def get_longest_run(lst):
    curr_len, run_span = 0, 0
    for k, gr in groupby(lst):
        len_ = len(list(gr))
        if (run_span and len_ > (run_span[1] + 1) - run_span[0]) or len_ > curr_len:
            run_span = (curr_len, curr_len + len_ - 1)
        curr_len += len_

    return run_span

lst = [False, False, True, False, False, False, False, True, True, False, False]
print(get_longest_run(lst))   # (3, 6)

---

Time performance comparison (to previous answer):

In [144]: lst = [False, False, True, False, False, False, False, True, True, False, False]                                   

In [145]: def get_longest_run_deniel(lst): 
     ...:     start = 0 
     ...:     runs = [] 
     ...:     for key, run in groupby(lst): 
     ...:         length = sum(1 for _ in run) 
     ...:         runs.append((start, start + length - 1)) 
     ...:         start += length 
     ...:  
     ...:     result = max(runs, key=lambda x: x[1] - x[0]) 
     ...:     return result 
     ...:                                                                                                                    

In [146]: def get_longest_run(lst): 
     ...:     curr_len, run_span = 0, 0 
     ...:     for k, gr in groupby(lst): 
     ...:         len_ = len(list(gr)) 
     ...:         if (run_span and len_ > (run_span[1] + 1) - run_span[0]) or len_ > curr_len: 
     ...:             run_span = (curr_len, curr_len + len_ - 1) 
     ...:         curr_len += len_ 
     ...:  
     ...:     return run_span 
     ...:                                                                                                                    

In [147]: %timeit get_longest_run_deniel(lst)                                                                                
6.06 µs ± 168 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)

In [148]: %timeit get_longest_run(lst)                                                                                       
3.67 µs ± 131 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)