Consider the following Python program, where x is assumed to be a list of integers.

def mystery_func(x):

n = len(x)

for i in range(n - 1):

for j in range(i + 1, n):

if x[j] - x[i] < j - i: return False

return True

3a. In plain English, describe what it accomplishes (i.e., the relationship between input and output, not how the code works).

3b. Analyze the running time and express it with big O.

3c. Rewrite this function so it accomplishes the same thing but is more efficient, and state the running time in a comment.