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Tested Python solution for LeetCode 38 with 14 pytest cases. Generate a practice environment with lcpy.
lcpy gen -n 38 # by problem number
lcpy gen -s count_and_say # by problem name
countAndSay(1) = "1"countAndSay(n) is the run-length encoding of countAndSay(n - 1)."3322251" we replace "33" with "23", replace "222" with "32", replace "5" with "15", and replace "1" with "11". Thus the compressed string becomes "23321511".
Given a positive integer n, return the nth element of the count-and-say sequence.
Input: n = 4
Output: "1211"
Explanation:
countAndSay(1) = "1"
countAndSay(2) = RLE of "1" = "11"
countAndSay(3) = RLE of "11" = "21"
countAndSay(4) = RLE of "21" = "1211"
Input: n = 1
Output: "1"
Explanation:
This is the base case.
class Solution:
# Time: O(n * L) where L is the length of the resulting string
# Space: O(L)
def count_and_say(self, n: int) -> str:
s = "1"
for _ in range(n - 1):
parts: list[str] = []
i = 0
while i < len(s):
j = i
while j < len(s) and s[j] == s[i]:
j += 1
parts.append(str(j - i))
parts.append(s[i])
i = j
s = "".join(parts)
return s
| Time | Space |
|---|---|
| O(n * L) where L is the length of the resulting string | O(L) |