n=int(input())
s='0'+input()
m=int(input())
mp=[[] for i in range(n+1)]
for i in range(m):
a,b=map(int,input().split())
a+=1
b+=1
mp[a].append(b)
import sys
sys.setrecursionlimit(100000000)
dfn=[0 for i in range(n+1)]
low=[0 for i in range(n+1)]
cnt=0
stk=[]
instk=[0 for i in range(n+1)]
p=0
scc=[0 for i in range(n+1)]
def tarjan(x):
global cnt,p
cnt+=1
dfn[x]=low[x]=cnt
stk.append(x)
instk[x]=1
for i in mp[x]:
if dfn[i]==0:
tarjan(i)
low[x]=min(low[x],low[i])
elif instk[i]:
low[x]=min(low[x],dfn[i])
if dfn[x]==low[x]:
p+=1
y=stk.pop()
instk[y]=0
scc[y]=p
while x!=y:
y = stk.pop()
instk[y] = 0
scc[y] = p
for i in range(1,n+1):
if dfn[i]==0:tarjan(i)
del instk,low,dfn
ru=[0 for i in range(p+1)]
h=[0 for i in range(p+1)]
l=[0 for i in range(p+1)]
nmp=[[] for i in range(p+1)]
for i in range(1,n+1):
if s[i]=='0': h[scc[i]]+=1
else : l[scc[i]]+=1
for j in mp[i]:
if scc[i]!=scc[j]:
ru[scc[j]]+=1
nmp[scc[i]].append(scc[j])
del mp
def dfs(x,a,b):
ans=0
vis=0
for y in nmp[x]:
ans=max(dfs(y,a+h[y],b+l[y]),ans)
vis=1
if vis==0:return min(a,b)
else:return ans
ans=0
for i in range(1,p+1):
if ru[i]==0:
ans=max(ans,dfs(i,h[i],l[i]))
print(ans)
宝石收集,tarjan
WA==Wonderful Answer2024-05-27 15:06
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