最近两道题TLE, 把 sort 改成 stable_sort 就过了， 所以总结一下。
cplusplus.com 上没有说 stable_sort 的实现算法， stable 是稳定的意思, 也许使用的是归并排序
在大多数测试中， stable_sort 的速度快于 sort, 但内存大于 sort
第一条 stable_sort， 第二条 sort
NOI Linux 测试 (1000万个元素排序， 仅测量排序函数所耗时间)
| 函数名称 | 数据性质 | 时间(s) |
|---|---|---|
| sort | 严格升序 | 0.729362 |
| sort | 严格降序 | 0.549648 |
| sort | [0, RAND_MAX]随机 | 1.998072 |
| sort | [0, 10]随机 | 1.352847 |
| sort | 全为1 | 1.246581 |
| stable_sort | 严格升序 | 0.505621 |
| stable_sort | 严格降序 | 0.900720 |
| stable_sort | [0, RAND_MAX]随机 | 1.706570 |
| stable_sort | [0, 10]随机 | 1.004860 |
| stable_sort | 全为1 | 0.508155 |
对于 sort 的描述
On average, linearithmic in the distance between first and last: Performs approximately (N*log2(N)) (where (N) is this distance) comparisons of elements, and up to that many element swaps (or moves).
对于 stable_sort 的描述
If enough extra memory is available, linearithmic in the distance between first and last: Performs up to (N*log_2(N)) element comparisons (where (N) is this distance), and up to that many element moves.
Otherwise, polyloglinear in that distance: Performs up to (N*log_2^2(N)) element comparisons, and up to that many element swaps.