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题目 https://cn.vjudge.net/problem/URAL-1133
题意 给你斐波那契数的某两项,求第n项
思路 暴力二分给的下标小的的第二项 用另一个验证
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
ll a[10000];
ll x1,x2,x3,y1,y2;
int ok(ll x)
{
a[x1] = y1;
a[x1+1] = x;
for(ll i=x1+2;i<=x2;i++)
{
a[i] = a[i-1] + a[i-2];
if(a[i] > 2e9) return 1;
else if(a[i] < -2e9) return -1;
}
if(y2 < a[x2]) return 1;
else if(y2 > a[x2]) return -1;
return 0;
}
ll solve(ll x)
{
a[x1] = y1,a[x1+1] = x;
if(x3 > x1)
{
for(ll i=x1+2;i<=x3;i++)
{
a[i] = a[i-1] + a[i-2];
}
return a[x3];
}
else
{
for(ll i=x1-1;i>=x3;i--)
{
a[i] = a[i+2] - a[i+1];
}
return a[x3];
}
}
int main()
{
ll n,m,i,j;
scanf("%lld%lld%lld%lld%lld",&x1,&y1,&x2,&y2,&x3);
x1 += 3000,x2 += 3000,x3 += 3000;
if(x1 > x2)
{
swap(x1,x2);
swap(y1,y2);
}
ll l = -2e9,r = 2e9;
while(r > l + 1)
{
ll mid = (l+r)/2;
if(ok(mid) > 0)
{
r = mid;
}
else if(ok(mid) < 0)
{
cout<<mid<<endl;
l = mid;
}
else
{
ll ans = solve(mid);
printf("%lld\n",ans);
break;
}
}
return 0;
}