<p>We consider a generalisation of the classical coupon collector problem. We define a super-coupon to be any <i>s</i>-subset of a universe of <i>n</i> coupons. In each round, a random <i>r</i>-subset from the universe is drawn and all its <i>s</i>-subsets are marked as collected. We show that the time to collect all super-coupons is <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10959_2025_1417_Article_IEq1.gif" Format="GIF" Height="48" Rendition="HTML" Resolution="72" Type="Linedraw" Width="252" /> </InlineMediaObject> <EquationSource Format="TEX">\((1 + o(1)) \left( {\begin{array}{c}r\\ s\end{array}}\right) ^{-1}\left( {\begin{array}{c}n\\ s\end{array}}\right) \log \left( {\begin{array}{c}n\\ s\end{array}}\right) \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mo>+</mo> <mi>o</mi> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">)</mo> </mrow> <msup> <mfenced close=")" open="("> <mrow> <mtable> <mtr> <mtd> <mi>r</mi> </mtd> </mtr> <mtr> <mtd> <mrow> <mrow /> <mi>s</mi> </mrow> </mtd> </mtr> </mtable> </mrow> </mfenced> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mfenced close=")" open="("> <mrow> <mtable> <mtr> <mtd> <mi>n</mi> </mtd> </mtr> <mtr> <mtd> <mrow> <mrow /> <mi>s</mi> </mrow> </mtd> </mtr> </mtable> </mrow> </mfenced> <mo>log</mo> <mfenced close=")" open="("> <mrow> <mtable> <mtr> <mtd> <mi>n</mi> </mtd> </mtr> <mtr> <mtd> <mrow> <mrow /> <mi>s</mi> </mrow> </mtd> </mtr> </mtable> </mrow> </mfenced> </mrow> </math></EquationSource> </InlineEquation> on average and has a Gumbel limit after a suitable normalisation. In a similar vein, we show that for any <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10959_2025_1417_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="69" /> </InlineMediaObject> <EquationSource Format="TEX">\(\alpha \in (0, 1)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>α</mi> <mo>∈</mo> <mo stretchy="false">(</mo> <mn>0</mn> <mo>,</mo> <mn>1</mn> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>, the expected time to collect <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10959_2025_1417_Article_IEq3.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="54" /> </InlineMediaObject> <EquationSource Format="TEX">\((1 - \alpha )\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mo>-</mo> <mi>α</mi> <mo stretchy="false">)</mo> </mrow> </math></EquationSource> </InlineEquation>-proportion of all super-coupons is <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10959_2025_1417_Article_IEq4.gif" Format="GIF" Height="48" Rendition="HTML" Resolution="72" Type="Linedraw" Width="232" /> </InlineMediaObject> <EquationSource Format="TEX">\((1 + o(1)) \left( {\begin{array}{c}r\\ s\end{array}}\right) ^{-1}\left( {\begin{array}{c}n\\ s\end{array}}\right) \log \left( {\frac{1}{\alpha }}\right) \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mo>+</mo> <mi>o</mi> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">)</mo> </mrow> <msup> <mfenced close=")" open="("> <mrow> <mtable> <mtr> <mtd> <mi>r</mi> </mtd> </mtr> <mtr> <mtd> <mrow> <mrow /> <mi>s</mi> </mrow> </mtd> </mtr> </mtable> </mrow> </mfenced> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> <mfenced close=")" open="("> <mrow> <mtable> <mtr> <mtd> <mi>n</mi> </mtd> </mtr> <mtr> <mtd> <mrow> <mrow /> <mi>s</mi> </mrow> </mtd> </mtr> </mtable> </mrow> </mfenced> <mo>log</mo> <mfenced close=")" open="("> <mfrac> <mn>1</mn> <mi>α</mi> </mfrac> </mfenced> </mrow> </math></EquationSource> </InlineEquation>. The <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10959_2025_1417_Article_IEq5.gif" Format="GIF" Height="10" Rendition="HTML" Resolution="72" Type="Linedraw" Width="42" /> </InlineMediaObject> <EquationSource Format="TEX">\(r = s\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>r</mi> <mo>=</mo> <mi>s</mi> </mrow> </math></EquationSource> </InlineEquation> case of this model is equivalent to the classical coupon collector model. We also consider a temporally dependent model where the <i>r</i>-subsets are drawn according to the following Markovian dynamics: the <i>r</i>-subset at round <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10959_2025_1417_Article_IEq6.gif" Format="GIF" Height="15" Rendition="HTML" Resolution="72" Type="Linedraw" Width="39" /> </InlineMediaObject> <EquationSource Format="TEX">\(k + 1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <mo>+</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation> is formed by replacing a random coupon from the <i>r</i>-subset drawn at round <i>k</i> with another random coupon from outside this <i>r</i>-subset. We link the time it takes to collect all super-coupons in the <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10959_2025_1417_Article_IEq5.gif" Format="GIF" Height="10" Rendition="HTML" Resolution="72" Type="Linedraw" Width="42" /> </InlineMediaObject> <EquationSource Format="TEX">\(r = s\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>r</mi> <mo>=</mo> <mi>s</mi> </mrow> </math></EquationSource> </InlineEquation> case of this model to the cover time of random walk on a certain finite regular graph and conjecture that in general, it takes <InlineEquation ID="IEq8"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10959_2025_1417_Article_IEq8.gif" Format="GIF" Height="48" Rendition="HTML" Resolution="72" Type="Linedraw" Width="260" /> </InlineMediaObject> <EquationSource Format="TEX">\((1 + o(1)) {{\frac{r}{s}}\left( {\begin{array}{c}r\\ s\end{array}}\right) ^{-1}}\left( {\begin{array}{c}n\\ s\end{array}}\right) \log \left( {\begin{array}{c}n\\ s\end{array}}\right) \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mo>+</mo> <mi>o</mi> <mrow> <mo stretchy="false">(</mo> <mn>1</mn> <mo stretchy="false">)</mo> </mrow> <mo stretchy="false">)</mo> </mrow> <mrow> <mfrac> <mi>r</mi> <mi>s</mi> </mfrac> <msup> <mfenced close=")" open="("> <mrow> <mtable> <mtr> <mtd> <mi>r</mi> </mtd> </mtr> <mtr> <mtd> <mrow> <mrow /> <mi>s</mi> </mrow> </mtd> </mtr> </mtable> </mrow> </mfenced> <mrow> <mo>-</mo> <mn>1</mn> </mrow> </msup> </mrow> <mfenced close=")" open="("> <mrow> <mtable> <mtr> <mtd> <mi>n</mi> </mtd> </mtr> <mtr> <mtd> <mrow> <mrow /> <mi>s</mi> </mrow> </mtd> </mtr> </mtable> </mrow> </mfenced> <mo>log</mo> <mfenced close=")" open="("> <mrow> <mtable> <mtr> <mtd> <mi>n</mi> </mtd> </mtr> <mtr> <mtd> <mrow> <mrow /> <mi>s</mi> </mrow> </mtd> </mtr> </mtable> </mrow> </mfenced> </mrow> </math></EquationSource> </InlineEquation> time on average to collect all super-coupons.</p>

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On a Generalisation of the Coupon Collector Problem

  • Siva Athreya,
  • Satyaki Mukherjee,
  • Soumendu Sundar Mukherjee

摘要

We consider a generalisation of the classical coupon collector problem. We define a super-coupon to be any s-subset of a universe of n coupons. In each round, a random r-subset from the universe is drawn and all its s-subsets are marked as collected. We show that the time to collect all super-coupons is \((1 + o(1)) \left( {\begin{array}{c}r\\ s\end{array}}\right) ^{-1}\left( {\begin{array}{c}n\\ s\end{array}}\right) \log \left( {\begin{array}{c}n\\ s\end{array}}\right) \) ( 1 + o ( 1 ) ) r s - 1 n s log n s on average and has a Gumbel limit after a suitable normalisation. In a similar vein, we show that for any \(\alpha \in (0, 1)\) α ( 0 , 1 ) , the expected time to collect \((1 - \alpha )\) ( 1 - α ) -proportion of all super-coupons is \((1 + o(1)) \left( {\begin{array}{c}r\\ s\end{array}}\right) ^{-1}\left( {\begin{array}{c}n\\ s\end{array}}\right) \log \left( {\frac{1}{\alpha }}\right) \) ( 1 + o ( 1 ) ) r s - 1 n s log 1 α . The \(r = s\) r = s case of this model is equivalent to the classical coupon collector model. We also consider a temporally dependent model where the r-subsets are drawn according to the following Markovian dynamics: the r-subset at round \(k + 1\) k + 1 is formed by replacing a random coupon from the r-subset drawn at round k with another random coupon from outside this r-subset. We link the time it takes to collect all super-coupons in the \(r = s\) r = s case of this model to the cover time of random walk on a certain finite regular graph and conjecture that in general, it takes \((1 + o(1)) {{\frac{r}{s}}\left( {\begin{array}{c}r\\ s\end{array}}\right) ^{-1}}\left( {\begin{array}{c}n\\ s\end{array}}\right) \log \left( {\begin{array}{c}n\\ s\end{array}}\right) \) ( 1 + o ( 1 ) ) r s r s - 1 n s log n s time on average to collect all super-coupons.