PAT 甲級 1050.String Subtraction C++/Java

題目來源

Given two strings S1 and S2, S=S1−S2 is defined to be the remaining string after taking all the characters in S2 from S1. Your task is simply to calculate S1−S2 for any given strings. However, it might not be that simple to do it fast.

Input Specification:

Each input file contains one test case. Each case consists of two lines which gives S1 and S2, respectively. The string lengths of both strings are no more than 104. It is guaranteed that all the characters are visible ASCII codes and white space, and a new line character signals the end of a string.

Output Specification:

For each test case, print S1−S2 in one line.

Sample Input:

They are students.
aeiou

Sample Output:

Thy r stdnts.

題意：

給兩個字符串s1，s2，計算s1-s2（在s1中刪除掉s2中出現過的字符）

分析：

• s2的字符存入哈希map
• 遍歷s1，看是否在map中出現
  • 出現：不輸出
  • 沒出現：輸出

c++實現：

#include <iostream>
#include <unordered_map>
#include <string>

using namespace std;
int main() {
    string s1, s2;
    getline(cin, s1);
    getline(cin, s2);
    unordered_map<char, int> charMap;
    for (int i = 0; i < s2.size(); ++i) {
        charMap[s2[i]] = 1;
    }
    for (int i = 0; i < s1.size(); ++i) {
        if (charMap[s1[i]] != 1) {
            cout << s1[i];
        }
    }
    return 0;
}

Java實現：