89 lines
1.6 KiB
C++
89 lines
1.6 KiB
C++
#include "pascal_triangle.h"
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#include <cstdio>
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using namespace ogu;
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PascalTriangle ptriang;
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void PascalRow::setFromPrevious(const PascalRow& prev)
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{
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k = prev.k + 1;
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clear();
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prolong(prev);
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}
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/** This prolongs the PascalRow. If it is empty, we set the first item
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* to k+1, which is noverk(k+1,k) which is the second item in the real
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* pascal row, which starts from noverk(k,k)=1. Then we calculate
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* other items from the provided row which must be the one with k-1.*/
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void PascalRow::prolong(const PascalRow& prev)
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{
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if (size() == 0)
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push_back(k+1);
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int last = back();
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for (unsigned int i = size(); i < prev.size(); i++) {
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last += prev[i];
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push_back(last);
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}
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}
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void PascalRow::prolongFirst(int n)
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{
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// todo: check n = 1;
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for (int i = (int)size()+2; i <= n; i++)
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push_back(i);
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}
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void PascalRow::print() const
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{
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printf("k=%d\n",k);
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for (unsigned int i = 0; i < size(); i++)
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printf("%d ",operator[](i));
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printf("\n");
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}
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int PascalTriangle::max_n() const
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{
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return (int)(tr[0].size()+1);
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}
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int PascalTriangle::max_k() const
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{
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return (int)tr.size();
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}
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void PascalTriangle::ensure(int n, int k)
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{
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// add along n
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if (n > max_n()) {
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tr[0].prolongFirst(n);
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for (int i = 2; i <= max_k(); i++)
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tr[i-1].prolong(tr[i-2]);
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}
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if (k > max_k()) {
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for (int i = max_k()+1; i <= k; i++) {
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PascalRow r;
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tr.push_back(r);
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tr.back().setFromPrevious(tr[i-2]);
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}
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}
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}
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int PascalTriangle::noverk(int n, int k)
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{
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// todo: rais if out of bounds
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if (n-k < k)
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k = n-k;
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if (k == 0)
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return 1;
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ensure(n, k);
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return (tr[k-1])[n-1-k];
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}
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void PascalTriangle::print() const
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{
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for (unsigned int i = 0; i < tr.size(); i++)
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tr[i].print();
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}
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