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