Codeforces Global Round 13 C題（差分）

https://codeforces.com/contest/1491/problem/C

貪心，從左往右每一輪只需要每個長度跳第一次，可以用差分數組維護每個點被踩的次數。

 1 #define IO std::ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
 2 #define bug(x) cout<<#x<<" is "<<x<<endl
 3 #include <bits/stdc++.h>
 4 #define iter ::iterator
 5 using namespace  std;
 6 typedef long long ll;
 7 typedef pair<int,ll>P;
 8 #define pb push_back
 9 #define mk make_pair
10 #define se second
11 #define fi first
12 #define rs o*2+1
13 #define ls o*2
14 const ll inf=1e18;
15 const int N=2e5+5;
16 int T;
17  
18 int n,cnt;
19  
20 ll a[N],b[N],c[N];
21 
22  
23 int main(){
24     IO;
25     cin>>T;
26     while(T--){
27         int f=0;
28         cin>>n;
29         for(int i=1;i<=n;i++){
30             cin>>a[i];
31             b[i]=0;
32         }
33         ll ans=0;
34         
35         for(int i=1;i<=n;i++){
36             b[i]+=b[i-1];
37             b[i+2]++;
38             int r=i+a[i]-1;
39             if(r<=n)b[i+a[i]+1]--;
40             ans+=max(0ll,a[i]-b[i]-1);
41             if(b[i]-a[i]+1>0){
42                 b[i+1]+=b[i]-a[i]+1;
43                 b[i+2]-=b[i]-a[i]+1;
44             }
45         }
46 
47 
48         cout<<ans<<endl;
49     }
50  
51 }
52 /*
53 18
54 6 6 5 4 3 3 3 2 3 5 2 10 7 6 1 1 10 2
55 
56 
57 
58 1 4 2 2 2 2 2
59 
60 1 3 2 2 2 1 2
61 
62 1 2 2 2 1 1 1
63 
64 1 1 2 1 1 1 1
65 
66 
67 */