AtCoder Regular Contest 084 C - Snuke Festival【二分】

C - Snuke Festival

....最后想到了，可是不应该枚举a[]，这样要二重循环，而应该枚举b[],这样只需一重循环。。。

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 using namespace std;
 typedef long long ll;
 const int maxn=1e5+;
 int a[maxn],b[maxn],c[maxn];
 int n;

 int FindLastSmaller(int key)
 {
     int l=,r=n-;
     while(l<=r){
         int mid=(l+r)>>;
         if(a[mid]>=key) r=mid-;
         else l=mid+;
     }
     return r;
 }

 int FindFirstLarger(int key)
 {
     int l=,r=n-;
     while(l<=r){
         int mid=(l+r)>>;
         if(c[mid]>key) r=mid-;
         else l=mid+;
     }
     return l;
 }

 int main()
 {
     cin>>n;
     for(int i=;i<n;i++) cin>>a[i];
     for(int i=;i<n;i++) cin>>b[i];
     for(int i=;i<n;i++) cin>>c[i];
     sort(a,a+n);
     sort(b,b+n);
     sort(c,c+n);
     ll ans=;
     for(int i=;i<n;i++){
         ll p1=FindLastSmaller(b[i]);
         ll p2=FindFirstLarger(b[i]);
         ans+=(p1+)*(n-p2);
     }
     cout<<ans<<endl;
     return ;
 }

lower_bound(),upper_bounder()不能再好用。。。

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 using namespace std;
 typedef long long ll;
 const int maxn = 1e5 + ;
 int a[maxn], b[maxn], c[maxn];
 int n;

 int main()
 {
     scanf("%d", &n);
     for (int i = ; i < n; i++) scanf("%d", &a[i]);
     for (int i = ; i < n; i++) scanf("%d", &b[i]);
     for (int i = ; i < n; i++) scanf("%d", &c[i]);
     sort(a, a + n);
     sort(b, b + n);
     sort(c, c + n);
     ll ans = ;
     for (int i = ; i<n; i++) {
         ll p = lower_bound(a, a + n, b[i]) - a;
         ll q = upper_bound(c, c + n, b[i]) - c;
         ans += p*(n - q);
     }
     printf("%lld\n", ans);
 }