思路
另线段树做法:https://www.cnblogs.com/fisherss/p/12287606.html
F题树状数组维护前缀即可
题目地址
https://ac.nowcoder.com/acm/contest/3004/F
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int maxn = 1e5+100;
int n;
char s[maxn];
const ll mod = 1e9+7;
struct bit{
ll c[maxn];
int lowbit(int x){
return x & -x;
}
void add(int pos,int v){
while(pos <= n){
c[pos] += v;
pos += lowbit(pos);
}
}
ll getsum(int pos){
ll res = 0;
while(pos){
res += c[pos];
pos -= lowbit(pos);
}
return res;
}
}pre,suf,cnt;
int main(){
cin>>n;
scanf("%s",s+1);
ll ans = 0;
for(int i=1;i<=n;i++){
if(s[i] == ‘1‘){
cnt.add(i,1);
pre.add(i,i);
ans = (ans + i*cnt.getsum(i) - pre.getsum(i))%mod;
}
}
cout<<ans<<endl;
return 0;
}
G题 3棵树状数组维护前缀和、后缀和、个数
题目地址
https://ac.nowcoder.com/acm/contest/3004/G
70%,wa
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int maxn = 1e5+100;
ll n;
char s[maxn];
const ll mod = 1e9+7;
struct bit{
ll c[maxn];
ll lowbit(ll x){
return x & -x;
}
void add(ll pos,ll v){
while(pos <= n){
c[pos] += v;
pos += lowbit(pos);
}
}
ll getsum(ll pos){
ll res = 0;
while(pos){
res += c[pos];
pos -= lowbit(pos);
}
return res;
}
}pre,suf,cnt;
void print(){
for(int i=1;i<=n;i++){
cout<<suf.getsum(i)<<" ";
}
cout<<endl;
}
int main(){
cin>>n;
scanf("%s",s+1);
ll ans = 0;
for(ll i=1;i<=n;i++){
if(s[i] == ‘1‘){
cnt.add(i,1);
pre.add(i,i);
suf.add(i,n-i+1);
ans = (ans + i*cnt.getsum(i) - pre.getsum(i))%mod;
}
}
cout<<ans%mod<<endl;
ll m;
cin>>m;
while(m--){
ll q,pos;
cin>>q>>pos;
if(q == 1){
//加点
cnt.add(pos,1);
pre.add(pos,pos);
suf.add(pos,n-pos+1);
//加上对前缀1的贡献影响
ans = (ans + (pos*cnt.getsum(pos) - pre.getsum(pos)))%mod;
//加上对后缀1的贡献影响
ans = (ans + ((n - pos + 1) * (cnt.getsum(n) - cnt.getsum(pos-1)) - (suf.getsum(n) - suf.getsum(pos-1))))%mod;
}else{
ans = (ans - (pos*cnt.getsum(pos) - pre.getsum(pos)))%mod;
ans = (ans - ((n - pos + 1) * (cnt.getsum(n) - cnt.getsum(pos-1)) - (suf.getsum(n) - suf.getsum(pos-1))))%mod;
cnt.add(pos,-1);
pre.add(pos,-pos);
suf.add(pos,-(n-pos+1));
}
cout<<ans%mod<<endl;
}
return 0;
}
原文地址:https://www.cnblogs.com/fisherss/p/12657814.html
时间: 2024-10-14 14:02:35