[[1, 5], [2, 4], [6, 8]]
[[1,5],[6,8]]
[[1, 3], [2, 6], [8, 10], [15, 18], [20, 22], [22, 25]]
[[1,6],[8,10],[15,18],[20,25]]
输入二维数组intervals的长度范围为1到10^4,每个线段的起点和终点满足0