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- import sys
- sys.stdin=open('tree.in','r')
- sys.stdout=open('tree.out','w')
- n=int(input())
- a= [[int(j) for j in input().split()] for i in range(n)]
- k1=0
- for i in range(n):
- for j in range(n):
- if a[i][j]==1:
- k1+=1
- visited=[False]*n
- def dfs(s):
- visited[s]=True
- for i in range(n):
- if a[s][i]==1 and visited[i]==False:
- visited[i]=True
- dfs(i)
- k=0
- l=0
- for i in range(n):
- if visited[i]==False:
- dfs(i)
- k+=1
- if k==1 and k1//2+1==n:
- print('YES')
- else:
- print('NO')
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