参考文章：
（1）Apollo6.0代码Lattice算法详解——Part 7: 获得最优轨迹
（2）Lattice算法详解

0 前言

  // 优选出cost最小的trajectory
  // 7. always get the best pair of trajectories to combine; return the first
  // collision-free trajectory.
  size_t constraint_failure_count = 0;
  size_t collision_failure_count = 0;
  size_t combined_constraint_failure_count =