When two same masses travelling in opposite directions with different velocities collide perfectly elastically, their velocities : 

Exchange

In this case also we need to conserve the momentum and write the expression for e. After doing so we will find that the sum of the initial velocities is equal to the sum of the final velocities. Same goes for the difference (with slight alterations). This will result in the final velocity of one body being equal to the initial velocity of the other. Hence, the velocities will get exchanged.