Sorting strings where some items are present but have zero length and some are absent

排序字符串，一些项存在但长度为零，一些不见了

youdao

The base case is whenever S1 or S2 is a zero-length string.

（基线条件（basecase）是S1或S2为长度为零的字符串的情形。

youdao

The base case is whenever S1 or S2 is a zero-length string.

（基线条件（basecase）是S1或S2为长度为零的字符串的情形。

youdao