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[Leetcode] Medium : Number of Provinces
[Leetcode] Medium : Number of Provinces
Description
There are n cities. Some of them are connected, while some are not. If city a is connected directly with city b, and city b is connected directly with city c, then city a is connected indirectly with city c.
A province is a group of directly or indirectly connected cities and no other cities outside of the group.
You are given an n x n matrix isConnected where isConnected[i][j] = 1 if the ith city and the jth city are directly connected, and isConnected[i][j] = 0 otherwise.
Return the total number of provinces.
Example 1:
Input: isConnected = [[1,1,0],[1,1,0],[0,0,1]]
Output: 2
Example 2:
Input: isConnected = [[1,0,0],[0,1,0],[0,0,1]]
Output: 3
My solution
class Solution: def findCircleNum(self, isConnected: List[List[int]]) -> int: # 특정 원소가 속한 집합을 찾기 def find_parent(parent, x): # 루트 노드를 찾을 때 까지 재귀 호출 if parent[x] != x : parent[x] = find_parent(parent, parent[x]) return parent[x] # 두 원소가 속한 집합을 합치기 def union_parent(parent, a, b): a = find_parent(parent, a) b = find_parent(parent, b) if a < b: parent[b] = a else: parent[a] = b v = len(isConnected) parent = [0] * v for i in range(v): parent[i] = i for i, con in enumerate(isConnected): for j, k in enumerate(con): if (k == 1) and (i != j): union_parent(parent, i, j) print(parent) s = set() for i in parent: s.add(find_parent(parent, i)) return len(s)
Other Solution
class DSU: def __init__(self, N): self.par = list(range(N)) def find(self, x): if self.par[x] != x: self.par[x] = self.find(self.par[x]) return self.par[x] def union(self, x, y): self.par[self.find(x)] = self.find(y) class Solution: def findCircleNum(self, isConnected: List[List[int]]) -> int: N = len(isConnected) dsu = DSU(N) for i in range(1, N): for j in range(i): if isConnected[i][j] == 1: dsu.union(i, j) s = set() for p in dsu.par: s.add(dsu.find(p)) return len(s)
기존에 짰던 코드가 오류가 계속 나타나 사람들이 풀이한 방법을 이용하였다. 기존 방법의 문제는 par리스트 자체를 return을 해 문제가 발생하였음을 확인할 수 있었고, 각 par리스트 안의 원소들의 parent를 찾아주면 정확한 결과를 낼 수 있다.
문제 출처 : https://leetcode.com/problems/number-of-provinces/
from http://ertt14.tistory.com/109 by ccl(A) rewrite - 2021-11-08 18:00:58