串S=""(空串),子串数目只有1种:""同样,当S="A",子串有"A"和""两个当S="AB",子串有 "A" "B" "AB" ""当S="ABC"子串有 "A" "B" "C" "AB" "AC" "BC" "ABC" ""S="ABC" 其实就是 S[]={'A','B','C','\0'}引入排列组合中的运...