Submission #881440

#	Time	Username	Problem	Language	Result	Execution time	Memory
881440		arashMLG	Fancy Fence (CEOI20_fancyfence)	C++17	100 / 100	30 ms	19656 KiB

fancyfence

#include<bits/stdc++.h>
#ifdef LOCAL
#include "Essentials/algo/debug.h"
#else
#define debug(...) 69
#endif
using namespace std;
 
typedef long long     ll;
typedef pair<int,int> pii;
 
const int N = 5e5 + 23;
const ll mod = 1e9 + 7;
const ll inf = 1e18;
 
#define F           first
#define S           second
#define pb          push_back
#define kill(x)     cout<<x<<endl, exit(0);
#define all(x)      x.begin(),x.end()
#define sz(x)       (int)x.size()
#define lc          (v << 1)
#define rc          ((v<<1) |1)
#define int         ll
 
void ok(int &x) {
	while(x <0) x += mod;
	x %=mod;
}
 
int pw(int a,int b) {
	int ans=1;
	while(b) {
		if(b&1) ok(ans *= a);
		b >>=1;
		ok(a *= a);		
	}
	return ans;
}
 
int n;
int h[N],w[N];
int l[N],r[N];
stack<int> st;
int ps[N];
 
int tedad =0;
 
int32_t main() {
    cin.tie(nullptr)->sync_with_stdio(false);
	cin>>n;
	for(int i = 1; i<= n ; i++) cin>>h[i];
	for(int i = 1; i<= n ; i++) cin>>w[i];
	for(int i = 1; i<= n ; i++) {
		if(w[i] == 0) continue;
		tedad ++;
		for(int j = i+1; j <=n ; j ++) {
			if(h[j] == h[i]) {
				ok(w[i] += w[j]);
				w[j] = 0;
				h[j] = inf;
			} else break;
		}
	}
	int tinv = pw(2,mod-2);
	for(int i = 1; i<= n+1 ; i++) {
		ok(ps[i] = w[i] + ps[i-1]);
	}
	int ans=0;
	h[0] = 0,h[n+1] = 0;
	st.push(0);
	for(int i = 1; i<= n; i++) {
		if(w[i] == 0) continue;
		while(h[st.top()] >= h[i]) st.pop();
		l[i] = st.top();
		st.push(i);
	} while(sz(st)) st.pop();
	st.push(n+1);
	for(int i = n; i >= 1; i--) {
		if(w[i] == 0) continue;
		while(h[st.top()] > h[i]) st.pop();
		r[i] = st.top();
		st.push(i);
	}
	
	for(int i = 1; i<= n ; i++) {
		if(w[i] == 0) continue;
		int x = (h[i] * (h[i]+1)%mod*tinv%mod) %mod;
		//ok(ans += (w[i] * (w[i]+1)%mod*tinv%mod) %mod * x %mod);
		int one = (ps[i-1]- ps[l[i]] + 2 * mod) %mod;
		int two = (ps[r[i]-1] - ps[i]  + 2 *mod) %mod; 
		debug(one,two,x);
		int f = (ps[r[i]-1] - ps[l[i]] + 2 * mod) %mod;
		int three = f * (f+1)%mod*tinv%mod;
		ok(three -= one * (one+1)%mod * tinv%mod);
		ok(three -= two*(two+1) %mod * tinv%mod);
		ok(ans += three *x );
		//ok(ans -= x);
	}
	cout<<ans%mod << '\n';
	return 0;
}

Compilation message (stderr)

fancyfence.cpp: In function 'int32_t main()':
fancyfence.cpp:5:20: warning: statement has no effect [-Wunused-value]
    5 | #define debug(...) 69
      |                    ^~
fancyfence.cpp:92:3: note: in expansion of macro 'debug'
   92 |   debug(one,two,x);
      |   ^~~~~

• Subtask 1: 0 / 0
• Subtask 2: 12 / 12
• Subtask 3: 13 / 13
• Subtask 4: 15 / 15
• Subtask 5: 15 / 15
• Subtask 6: 18 / 18
• Subtask 7: 27 / 27