31 lines
575 B
C
31 lines
575 B
C
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#include <stdio.h>
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unsigned long long c(int n, int m);
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int main(void){
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unsigned long long q[21]={0,0,1,2},q2[21]={0,0,1},temp = 1;
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int i;
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for(i = 4; i <= 20; i++){
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q2[i-1] = q[i-2] + (i-2) * q2[i-2];
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q[i] = (i-1) * q2[i-1];
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}
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int numbers,m,n;
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scanf("%d",&numbers);
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for(i = 0; i < numbers; i++){
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scanf("%d %d",&n,&m);
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printf("%llu\n",c(n,m) * q[m]);
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}
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return 0;
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}
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unsigned long long c(int n, int m){
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int i = 0;
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unsigned long long temp = 1, temp2 = 1;
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if(m > n/2) m = n-m;
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for(i = 0; i < m; i++){
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temp *= n-i;
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temp2 *= i+1;
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}
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return temp/temp2;
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}
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