C++ :

#include <iostream>
using namespace std;
int main() {
    int balance = 100; // 初始存款
    int target=200;        // 目标金额
    int save_amount=50;   // 每周存款金额
    int withdraw_amount=20; // 每周取款金额
    int weeks = 0;     // 存钱的周数
    while (balance < target) {
        balance += save_amount;  // 每周存钱
        weeks++;
        balance -= withdraw_amount; // 每周取钱
    }
    cout << weeks;
    return 0;
}