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    <p>I'm writing a program to find if I can make a square with N sticks of N length. Ive used Bitmask cause its easier for the big input I'm gonna put in there. For some reason, my backtracking code its not returning anything, in this line "bitmask &amp; (1 &lt;&lt; vec[i])" it never goes in. Can someone help me if im using the wrong functions? I've recently learned this, but I cant find info. </p> <p>PD:im not an english speaker, sorry for my grammar and syntax problems.</p> <p>Thanks</p> <pre><code>// 10364 - Square.cpp: archivo de proyecto principal. #include "stdafx.h" #include &lt;stdio.h&gt; #include &lt;vector&gt; using namespace std; vector&lt;int&gt; vec; int bitmask,casos,palitos,suma,maximo; bool analiza(int analizado,int lados)// lados =cantidad lados analizados, contador { if (analizado==maximo) { analizado=0; lados++; } if(lados==4) { printf("yes\n"); return true; } for (int i=0;i&lt;palitos;i++) { if (!(bitmask &amp; (1 &lt;&lt; i))) { if (analizado+vec[i]&lt;=maximo) { bitmask | (1 &lt;&lt; i); if(analiza(analizado+1,lados)) return true; bitmask &amp; ~(1 &lt;&lt; i); } } } return false; //prender: bitmask | (1 &lt;&lt; indice) //apagar: bitmask &amp; ~(1 &lt;&lt; indice) /*comparar: bitmask &amp; (1 &lt;&lt; indice)*/ } int main() { freopen("in.txt","rt",stdin); freopen("out.txt","wt",stdout); scanf("%d\n",&amp;casos); for(int i=0;i&lt;casos;i++) { scanf("%d",&amp;palitos); vec.clear(); vec.resize(palitos); suma=0; for(int j=0;j&lt;palitos;j++) { scanf("%d",&amp;vec[j]); suma+=vec[j]; } if(suma%4!=0) printf("no\n"); else{ bitmask=0; maximo=suma/4; analiza(0,0); } } return 0; } </code></pre>
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