【leetcode】1286. Iterator for Combination
题目如下:
Design an Iterator class, which has:
- A constructor that takes a string
characters
of sorted distinct lowercase English letters and a numbercombinationLength
as arguments.- A function next() that returns the next combination of length
combinationLength
in lexicographical order.- A function hasNext() that returns
True
if and only if there exists a next combination.Example:
CombinationIterator iterator = new CombinationIterator("abc", 2); // creates the iterator. iterator.next(); // returns "ab"
iterator.hasNext(); // returns true
iterator.next(); // returns "ac"
iterator.hasNext(); // returns true
iterator.next(); // returns "bc"
iterator.hasNext(); // returns falseConstraints:
1 <= combinationLength <= characters.length <= 15
- There will be at most
10^4
function calls per test.- It's guaranteed that all calls of the function
next
are valid.
解题思路:全排列的问题,把所有排列预先计算出来即可。
代码 如下:
class CombinationIterator(object): def __init__(self, characters, combinationLength):
"""
:type characters: str
:type combinationLength: int
"""
self.val = []
from itertools import combinations
for i in combinations(characters, combinationLength):
self.val.append(''.join(i)) def next(self):
"""
:rtype: str
"""
return self.val.pop(0) def hasNext(self):
"""
:rtype: bool
"""
return len(self.val) > 0 # Your CombinationIterator object will be instantiated and called as such:
# obj = CombinationIterator(characters, combinationLength)
# param_1 = obj.next()
# param_2 = obj.hasNext()
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