Leetcode #158: Read N Characters Given read4 II - Call Multiple Times
In this guide, we solve Leetcode #158 Read N Characters Given read4 II - Call Multiple Times in Python and focus on the core idea that makes the solution efficient.
You will see the intuition, the step-by-step method, and a clean Python implementation you can use in interviews.
Problem Statement
Given a file and assume that you can only read the file using a given method read4, implement a method read to read n characters. Your method read may be called multiple times.
Quick Facts
- Difficulty: Hard
- Premium: Yes
- Tags: Array, Interactive, Simulation
Intuition
The rules are explicit, so simulating the process step by step is safest.
Careful state updates prevent subtle bugs.
Approach
Translate the rules into state updates and apply them in order.
Track the final state or aggregate as required.
Steps:
- Translate rules into state updates.
- Iterate for each step.
- Return the final state.
Example
Parameter: char[] buf4
Returns: int
buf4[] is a destination, not a source. The results from read4 will be copied to buf4[].
Python Solution
# The read4 API is already defined for you.
# def read4(buf4: List[str]) -> int:
class Solution:
def __init__(self):
self.buf4 = [None] * 4
self.i = self.size = 0
def read(self, buf: List[str], n: int) -> int:
j = 0
while j < n:
if self.i == self.size:
self.size = read4(self.buf4)
self.i = 0
if self.size == 0:
break
while j < n and self.i < self.size:
buf[j] = self.buf4[self.i]
self.i += 1
j += 1
return j
Complexity
The time complexity is O(n). The space complexity is O(1) to O(n).
Edge Cases and Pitfalls
Watch for boundary values, empty inputs, and duplicate values where applicable. If the problem involves ordering or constraints, confirm the invariant is preserved at every step.
Summary
This Python solution focuses on the essential structure of the problem and keeps the implementation interview-friendly while meeting the constraints.