question: private void mergeForceCollapse ( ) { while ( stackSize > 1 ) { int n = stackSize - 2 ; if ( n > 0 && runLen [ n - 1 ] < runLen [ n + 1 ] ) n -- ; mergeAt ( n ) ; } }
target:  Merges all runs on the stack until only one remains.  This method is called once, to complete the sort.