【CF#192 A】Funky Numbers (二分,查詢)
題幹:
As you very well know, this year's funkiest numbers are so called triangular numbers (that is, integers that are representable as , where k is some positive integer), and the coolest numbers are those that are representable as a sum of two triangular numbers.
A well-known hipster Andrew adores everything funky and cool but unfortunately, he isn't good at maths. Given number n
Input
The first input line contains an integer n (1 ≤ n ≤ 109).
Output
Print "YES" (without the quotes), if n can be represented as a sum of two triangular numbers, otherwise print "NO" (without the quotes).
Examples
Input
256
Output
YES
Input
512
Output
NO
Note
In the first sample number .
In the second sample number 512 can not be represented as a sum of two triangular numbers.
解題報告:
優秀的二分,複雜度sqrtnlogn
#include<bits/stdc++.h> using namespace std; int main() { int n; cin>>n; int tmp,key; int l ,r,mid; n*=2; for(int i = 1; i<=sqrt(n); i++) { tmp = i * (i+1); key = n-tmp; l = i; r = sqrt(n); while(l<=r) { mid = (l+r)/2; if(mid * (mid+1) < key) l=mid+1; else if(mid*(mid+1)>key) r = mid-1; else { printf("YES\n");return 0 ; } } } printf("NO\n"); return 0 ; }