Leetcode #2797: Partial Function with Placeholders
In this guide, we solve Leetcode #2797 Partial Function with Placeholders 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 function fn and an array args, return a function partialFn. Placeholders "_" in the args should be replaced with values from restArgs starting from index 0.
Quick Facts
- Difficulty: Easy
- Premium: Yes
- Tags: JavaScript
Intuition
We need to fill placeholders in order, then append any remaining arguments.
A single pass through args while consuming restArgs achieves this cleanly.
Approach
Build a new argument list by replacing each "_" with the next value from restArgs. After the scan, append any remaining restArgs, then call fn.
Steps:
- Iterate over
args, replacing"_"from an iterator overrestArgs. - Append leftover
restArgsto the end. - Call
fnwith the final argument list.
Example
Input: fn = (...args) => args, args = [2,4,6], restArgs = [8,10]
Output: [2,4,6,8,10]
Explanation:
const partialFn = partial(fn, args)
const result = partialFn(...restArgs)
console.log(result) // [2,4,6,8,10]
There are no placeholders "_" in args therefore restArgs is just added at the end of args. Then the elements of the args are passed as separate arguments to fn, which returns passed arguments as an array.
Python Solution
class Solution:
def partial(self, fn, args):
def partial_fn(*restArgs):
rest_iter = iter(restArgs)
merged = []
for a in args:
if a == "_":
try:
merged.append(next(rest_iter))
except StopIteration:
merged.append("_")
else:
merged.append(a)
merged.extend(list(rest_iter))
return fn(*merged)
return partial_fn
Complexity
The time complexity is , and the space complexity is .
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.