Find the nondecreasing subsequences

Time Limit: 10000/5000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 1072    Accepted Submission(s): 370

Problem Description
How many nondecreasing subsequences can you find in the sequence S = {s1, s2, s3, ...., sn} ? For example, we assume that S = {1, 2, 3}, and you can find seven nondecreasing subsequences, {1}, {2}, {3}, {1, 2}, {1, 3}, {2, 3}, {1, 2, 3}.
 
Input
The input consists of multiple test cases. Each case begins with a line containing a positive integer n that is the length of the sequence S, the next line contains n integers {s1, s2, s3, ...., sn}, 1 <= n <= 100000, 0 <= si <= 2^31.
 
Output
For each test case, output one line containing the number of nondecreasing subsequences you can find from the sequence S, the answer should % 1000000007.
 
Sample Input
3
1 2 3
 
Sample Output
7
 
Author
8600
 
Recommend
lcy
 
#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm> using namespace std; const int mod=;
const int N=; struct node{
int val,id;
}a[N]; int n,b[N],c[N],arr[N]; int lowbit(int x){
return x&(-x);
} void update(int i,int val){
while(i<=n){
arr[i]+=val;
arr[i]%=mod;
i+=lowbit(i);
}
} int Sum(int i){
int ans=;
while(i>){
ans+=arr[i];
ans%=mod;
i-=lowbit(i);
}
return ans;
} int cmp(node a,node b){
return a.val<b.val;
} int main(){ //freopen("input.txt","r",stdin); while(~scanf("%d",&n)){
memset(b,,sizeof(b));
memset(arr,,sizeof(arr));
for(int i=;i<=n;i++){
scanf("%d",&a[i].val);
a[i].id=i;
}
sort(a+,a+n+,cmp);
b[a[].id]=;
for(int i=;i<=n;i++)
if(a[i].val==a[i-].val)
b[a[i].id]=b[a[i-].id];
else
b[a[i].id]=i;
for(int i=;i<=n;i++){
c[i]=Sum(b[i]);
update(b[i],c[i]+);
}
printf("%d\n",Sum(n));
}
return ;
}

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