【PAT甲级真题】- String Subtraction (20)String Subtraction - PTA String Subtraction - 牛客Given two strings S 1 S_1 S1and S 2 , S = S 1 − S 2 S_2,S=S_1−S_2 S2,S=S1−S2is defined to be the remaining string after taking all the characters in S 2 S_2 S2from S 1 S_1 S1. Your task is simply to calculat