473. Matchsticks to Square
Đề Bài
You are given an integer array matchsticks where matchsticks[i] is the length of the ith matchstick. You want to use all the matchsticks to make one square. You should not break any stick, but you can link them up, and each matchstick must be used exactly one time.
Return true if you can make this square and false otherwise.
Example 1:
Input: matchsticks = [1,1,2,2,2] Output: true Explanation: You can form a square with length 2, one side of the square came two sticks with length 1.
Example 2:
Input: matchsticks = [3,3,3,3,4] Output: false Explanation: You cannot find a way to form a square with all the matchsticks.
Constraints:
1 <= matchsticks.length <= 151 <= matchsticks[i] <= 108
Thuật Toán & Kỹ Thuật
⏱️ Thời gian
O(n log n)
💾 Không gian
O(n)
Lời Giải
Python
0473-matchsticks-to-square.py
class Solution:
def makesquare(self, matchsticks: List[int]) -> bool:
total = sum(matchsticks)
if total % 4 != 0:
return False
n = len(matchsticks)
k = 4
self.d = total // k
flags = [0] * k
self.check = False
matchsticks.sort(reverse = True)
def backTracking(i):
if self.check:
return
if i == n:
self.check = True
return
seen = set()
for j in range(k):
if flags[j] in seen:
continue
if flags[j] + matchsticks[i] > self.d:
continue
seen.add(flags[j])
flags[j] += matchsticks[i]
backTracking(i + 1)
flags[j] -= matchsticks[i]
backTracking(0)
return self.check