title: find minimum dot product in a set of two-dimension vectors
body: <p>Suppose you have <code>n(n&lt;=50000)</code> two-dimension vectors <code>pi=(xi,yi)</code>,for every <code>1&lt;=i&lt;=n</code>,find <code>1&lt;=j&lt;=n</code> that <code>minimize dot(pi,pj)</code>,where <code>dot(pi,pj)=xi*xj+yi*yj</code>;</p>
  
  <p>Is there any solution can get the correct answer efficiently?
  upd:<code>|xi,yi|&lt;=100</code></p>