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poj2591 Set Definition(递推)
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题目链接:http://poj.org/problem?id=2591
Description
Set S is defined as follows:
(1) 1 is in S;
(2) If x is in S, then 2x + 1 and 3x + 1 are also in S;
(3) No other element belongs to S.
Find the N-th element of set S, if we sort the elements in S by increasing order.
(1) 1 is in S;
(2) If x is in S, then 2x + 1 and 3x + 1 are also in S;
(3) No other element belongs to S.
Find the N-th element of set S, if we sort the elements in S by increasing order.
Input
Input will contain several test cases; each contains a single positive integer N (1 <= N <= 10000000), which has been described above.
Output
For each test case, output the corresponding element in S.
Sample Input
100 254
Sample Output
418 1461
Source
POJ Monthly--2005.08.28,Static
代码如下:
#include <iostream> using namespace std; int a[10000017]; int main() { int i, two = 1, three = 1; a[1] = 1; for(i = 2; i <= 10000000; i++) { a[i] = min(a[two]*2+1,a[three]*3+1); if(a[i] == a[two]*2+1) two++; if(a[i] == a[three]*3+1) three++; } int n; while(cin >> n) { cout<<a[n]<<endl; } return 0; }
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