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https://github.com/Kiritow/OJ-Problems-Source.git
synced 2024-03-22 13:11:29 +08:00
21 lines
451 B
C++
21 lines
451 B
C++
#include <stdio.h>
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int main(){
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__int64 a[21] = {0, 0, 1}, p;
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int i, t;
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int n, m;
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for(i = 3; i < 21; i++){
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a[i] = (i - 1) * (a[i - 1] + a[i - 2]);
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}
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scanf("%d", &t);
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while(t--){
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p = 1;
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scanf("%d %d", &n, &m);
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for(i = n - m + 1; i <= n; i++)
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p *= i;
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for(i = 1; i <= m; i++)
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p /= i;
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printf("%I64d\n", p * a[m]);
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}
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return 0;
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}
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