二分查找可以偷个小懒~

#include<bits/stdc++.h>

using namespace std;

const int N = 1e5 + 5;
int num[N];

int main(void)
{
	int n;
	cin >> n;
	for (int i = 0; i < n; i++) cin >> num[i];
	
	int t;
	cin >> t;
	for (int k = 0; k < t; k++)
	{
		int x;
		cin >> x;

		if (x == 0)
		{
			int i;
			cin >> i;
			int a = lower_bound(num, num + n, i)-num;
			int b = upper_bound(num, num + n, i) - num-1;
			if (num[a] == num[b]) cout << b << endl;
			else cout << -1 << endl;
		}

		else if (x == 1)
		{
			int i;
			cin >> i;
			int a = lower_bound(num, num + n, i) - num;
			int b = upper_bound(num, num + n, i) - num - 1;
			if (num[a] == num[b]) cout << a << endl;
			else cout << -1 << endl;
		}

		else if (x == 2)
		{
			int j, k;
			cin >> j >> k;
			int a = lower_bound(num, num + n, j) - num;
			int b = upper_bound(num, num + n, k) - num - 1;
			if (num[n - 1] < j) cout << -1 << endl;
			else cout << b-a+1 << endl;
		}

		else if (x == 3)
		{
			int i;
			cin >> i;
			int a = upper_bound(num, num + n, i) - num;
			if (num[n - 1] < i) cout << -1 << endl;
			else cout << a << endl;
		}
		
		else if (x == 4)
		{
			int i;
			cin >> i;
			int a = lower_bound(num, num + n, i) - num-1;
			int b = lower_bound(num, num + n, num[a]) - num;
			if (num[n - 1] < i) cout << -1 << endl;
			else cout << b << endl;
		}

	}
	return 0;
}

芜湖起飞~

#include<bits/stdc++.h>
using namespace std;
const int N=1e6+5;
#define ll long long
ll f[N],x,y,z,l,r,n;
ll find0(ll g){
	l=1,r=n;
	while(l<=r){
		ll mid=(l+r)/2;
		if(f[mid]<=g){
			l=mid+1;
		}
		else{
			r=mid-1;
		}
	}
	if(f[l-1]==g){
		return l-2;
	}
	else{
		return -1;
	}
}
ll find1(ll g){
	l=1,r=n;
	while(l<=r){
		ll mid=(l+r)/2;
		if(f[mid]>=g){
			r=mid-1;
		}
		else{
			l=mid+1;
		}
	}
	if(f[l]==g){
		return l-1;
	}
	else{
		return -1;
	}
}
ll find3(ll g){
	l=1,r=n;
	while(l<=r){
		ll mid=(l+r)/2;
		if(f[mid]<=g){
			l=mid+1;
		}
		else{
			r=mid-1;
		}
	}
	if(f[l]>g){
		return f[l];
	}
	else{
		return -1;
	}
}
ll find4(int g){
	l=1,r=n;
	while(l<=r){
		ll mid=(l+r)/2;
		if(f[mid]>=g){
			r=mid-1;
		}
		else{
			l=mid+1;
		}
	}
	if(f[r]<g){
		return f[r];
	}
	else{
		return -1;
	}
}
ll findy(ll g){
	l=1,r=n;
	while(l<=r){
		ll mid=(l+r)/2;
		if(f[mid]<=g){
			l=mid+1;
		}
		else{
			r=mid-1;
		}
	}
	if(f[l-1]==g){
		return l-2;
	}
	else{
		return r;
	}
}
ll findz(ll g){
	l=1,r=n;
	while(l<=r){
		ll mid=(l+r)/2;
		if(f[mid]>=g){
			r=mid-1;
		}
		else{
			l=mid+1;
		}
	}
	if(f[l]==g){
		return l-1;
	}
	else{
		return r-1;
	}
}
int main(){
	cin>>n;
	for(ll i=1;i<=n;i++){
		cin>>f[i];
	}
	int t;
	cin>>t;
	while(t--){
		ll ans=0;
		cin>>x;
		if(x!=2){
			cin>>y;
			if(x==0){
				cout<<find0(y)<<endl;
			}
			if(x==1){
				cout<<find1(y)<<endl;
			}
			if(x==3){
				cout<<find3(y)<<endl;
			}
			if(x==4){
				cout<<find4(y)<<endl;
			}
		}
		else{
			cin>>y>>z;
			ans=findy(z)-findz(y)+1;
			cout<<ans<<endl;
		}
	}
	return 0;
}