Comet OJ - Contest #4 D求和 思维题

Code:

#include <bits/stdc++.h>
#define setIO(s) freopen(s".in","r",stdin)
#define ll long long
#define maxn 100000
using namespace std;
int arr[30],brr[maxn];
ll calc(ll t) {
    int n=0,m=0;
    while(t) arr[++n]=t%10,t/=10;
    while(n>=1) {
        for(int i=2;i<=n;++i) brr[++m]=(arr[i]+arr[i-1])%10;
        while(brr[m]==0 && m>=2) --m;
        for(int i=1;i<=m;++i) arr[i]=brr[i];
        n=m,m=0;
    }
    return arr[1];
}
ll solve(ll k) {
    if(k<10) return k*(k+1)/2;
    ll re=(k/10)*45,t=calc((k/10)*10);
    int o=k%10;
    for(int i=0;i<=o;++i) re+=1ll*(t+i)%10;
    return re;
}
int main() {
    // setIO("input");
    int T;
    scanf("%d",&T);
    while(T--) {
        ll l,r;
        scanf("%lld%lld",&l,&r);
        printf("%lld\n",solve(r) - solve(l-1));
    }
    return 0;
}