import java.io.*; import java.util.*;
public class FancyFence {
/**
*
* See analysis
*/
public static class Pair{
long h; long len;
public Pair(long a, long b){
this.h=a; this.len=b;
}
}
static long MOD=1000000007;
public static void main(String[] args) throws IOException {
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
int N=Integer.parseInt(br.readLine());
long[] h=new long[N]; long[] w=new long[N];
StringTokenizer st=new StringTokenizer(br.readLine());
for (int i = 0; i < N; i++) {
h[i]=Long.parseLong(st.nextToken());
}
st=new StringTokenizer(br.readLine());
for (int i = 0; i < N; i++) {
w[i]=Long.parseLong(st.nextToken());
}
long ans=0;
Stack<Pair> stk=new Stack<>();
long cur; long x,y,cur2,z;
for (int i = 0; i < N; i++) {
//Only count rectangles whose RIGHT SIDE lies in rectangle i
//Stack is monotonic: Pop everyone greater than h, add correspondingly
cur=0;//Tracks the width of stuff with height >h
while(!stk.isEmpty() &&stk.peek().h>h[i]){
cur+=(long) stk.pop().len; cur%=MOD;
}
//System.out.println(i+" "+cur);
//System.out.println("");
x=(long) h[i]*(h[i]+1)/2; x%=MOD;
cur*=x; cur%=MOD;
cur*=w[i]; cur%=MOD;
ans+=cur; ans%=MOD;
//Now count the rectangles in the current rectangle
y=(long) w[i]*(w[i]+1)/2; y%=MOD;
z=(x*y)%MOD;
ans+=z; ans%=MOD;
//Now (naively) count remaining rectangles in the stack, this can be sped up w/ prefix sum
if(!stk.isEmpty()){
//Merge sections
//For everyone in the stack, add some stuff
cur2=0;
for (Pair q: stk) {
z=(long) q.h*(q.h+1)/2; z%=MOD;
z*=q.len; z%=MOD;
cur2+=z; cur2%=MOD;
}
cur2*=w[i]; cur2%=MOD;
ans+=cur2; ans%=MOD;
Pair p=stk.pop();
stk.add(new Pair(p.h,p.len+cur));
stk.add(new Pair(h[i],w[i]));
}else{
stk.add(new Pair(h[i],w[i]+cur));
}
/*
System.out.println(i);
for (Pair j: stk) {
System.out.println(j.h+" "+j.len);
}
System.out.println(ans);
System.out.println("");
*/
}
System.out.println(ans%MOD);
}
}
Compilation message
fancyfence.java:2: error: class FancyFence is public, should be declared in a file named FancyFence.java
public class FancyFence {
^
1 error
