#include<stdio.h>
#include<set>
int d[600001];
int l[300001];
int ans[300001];
int p[300001], e[300001];
struct R
{
int s, e, n;
R(int _s, int _e, int _n):s(_s), e(_e), n(_n){}
};
bool operator<(const R &A, const R &B){return A.s<B.s;}
int root(int x){return p[x]==x?x:p[x]=root(p[x]);}
int uni(int a, int b){a=root(a);b=root(b);return p[b] = a;}
void chk(int a, int b)
{
a = root(a);
b = root(b);
if(e[a] != 0) uni(e[a], b);
if(e[b] != 0) a = uni(e[b], a);
e[a] = b = root(b);
e[b] = a;
}
int main()
{
int n, i;
int t;
scanf("%d", &n);
for(i=1; i<=n; i++) p[i] = i;
for(i=1; i<=2*n; i++)
{
scanf("%d", d+i);
l[d[i]] = i;
}
std::set<R> S;
for(i=1; i<=2*n; i++)
{
t = l[d[i]];
if(t == i) continue;
int s, end;
s=10000000; end = -1;
while(!S.empty() && S.begin()->e <= i) S.erase(S.begin());
auto it = S.begin();
for(; it != S.end() && it->e <= t; it=S.begin())
{
if(s > it->s) s = it->s;
if(end < it->e) end = it->e;
chk(d[i], it->n);
S.erase(S.begin());
}
if((S.size()!=0 && S.begin()->s <= t))
{
printf("IMPOSSIBLE\n");
return 0;
}
int tmp = root(d[i]);
if(e[tmp] == tmp)
{
printf("IMPOSSIBLE");
return 0;
}
if(end!=-1)
S.insert(R(s, end, e[d[i]]));
S.insert(R(t, t, d[i]));
}
// for(i=1; i<=n; i++) printf("%d %d\n", p[i], e[i]);
t = root(1);
for(i=1; i<=2*n; i++)
{
if(root(d[i]) == t) printf("^");
else
{
printf("v");
chk(d[i], t);
t = root(t);
}
}
return 0;
}
Compilation message
wire.cpp: In function 'int main()':
wire.cpp:43:3: warning: 'auto' will change meaning in C++0x; please remove it [-Wc++0x-compat]
wire.cpp:43:8: error: 'it' does not name a type
wire.cpp:44:9: error: 'it' was not declared in this scope
wire.cpp:28:17: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
wire.cpp:32:19: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
