使用比较器 java.lang.IllegalArgumentException: Comparison method violates its general contract! 解决办法

java.lang.IllegalArgumentException: Comparison method violates its general contract!
  at line 899, java.util.TimSort.mergeHi
  at line 516, java.util.TimSort.mergeAt
  at line 441, java.util.TimSort.mergeCollapse
  at line 245, java.util.TimSort.sort
  at line 1512, java.util.Arrays.sort
  at line 1462, java.util.ArrayList.sort
  at line 175, java.util.Collections.sort
  at line 37, Solution.merge
  at line 52, __DriverSolution__.__helper__
  at line 96, __Driver__.main

Collections.sort(intervals, new Comparator() {
        @Override
        public int compare(Interval o1, Interval o2) {
        if ( o1.start>o2.start) return 1;
        else return -1;
     }
});

上面代码报错都是因为我们比较器不够严谨，只有返回1和-1，米有返回0。将代码改为下面就正常了:

Collections.sort(intervals, new Comparator() {
          @Override
          public int compare(Interval o1, Interval o2) {  //必须有返回0的情况，否则报错
          if ( o1.start>o2.start) return 1;
          else if (o1.start==o2.start)return 0;
          else return -1;
     }
});