【CF1023B】Pair of Toys（解方程）

题意：给定n个玩具要你选出两个玩具求出k的价值，第i个玩具的价值为i。若是没有选择方案，输出0

补充：玩具A与玩具B 和玩具B和玩具A 是同一种选择

n,k<=1e14

思路：列出式子，解不等式组

 1 #include<cstdio>
 2 #include<cstring>
 3 #include<string>
 4 #include<cmath>
 5 #include<iostream>
 6 #include<algorithm>
 7 #include<map>
 8 #include<set>
 9 #include<queue>
10 #include<vector>
11 using namespace std;
12 typedef long long ll;
13 typedef unsigned int uint;
14 typedef unsigned long long ull;
15 typedef pair<int,int> PII;
16 typedef vector<int> VI;
17 #define fi first
18 #define se second 
19 #define MP make_pair
20 #define N   210000
21 #define MOD 1000000007
22 #define eps 1e-8 
23 #define pi acos(-1)
24 #define oo 2000000000
25 
26 
27 
28 int read()
29 { 
30    int v=0,f=1;
31    char c=getchar();
32    while(c<48||57<c) {if(c=='-') f=-1; c=getchar();}
33    while(48<=c&&c<=57) v=(v<<3)+v+v+c-48,c=getchar();
34    return v*f;
35 }
36 
37 void swap(int &x,int &y)
38 {
39     int t=x;x=y;y=t;
40 }
41 
42 
43 ll max(ll x,ll y)
44 {
45     if(x>y) return x;
46     return y;
47 }
48 
49 ll min(ll x,ll y)
50 {
51     if(x<y) return x;
52     return y;
53 }
54 
55 int main()
56 {
57 //    freopen("1.in","r",stdin);
58 //    freopen("1.out","w",stdout);
59     ll n,k;
60     scanf("%lld%lld",&n,&k);
61      ll s=max(1,max(k-n,k/2+1));
62      ll t=min(n,k-1);
63      if(s>t) printf("0");
64       else 
65       {
66           ll ans=t-s+1;
67         printf("%lld",ans);
68       }
69     
70     return 0;
71 }