2043. Simple Bank System

 C++

class Bank {
    vector<long long> balance;
    bool valid(int account) {
        return account > 0 && account <= balance.size();
    }
    bool enough(int account, long long money) {
        return balance[account - 1] >= money;
    }
public:
    Bank(vector<long long>& balance) : balance(balance) {}
    bool transfer(int from, int to, long long money) {
        if (valid(from) && valid(to) && enough(from, money)) {
            balance[from - 1] -= money;
            balance[to - 1] += money;
            return true;
        }
        return false;
    }
    bool deposit(int account, long long money) {
        if (valid(account)) {
            balance[account - 1] += money;
            return true;
        }
        return false;
    }
    bool withdraw(int account, long long money) {
        if (valid(account) && enough(account, money)) {
            balance[account - 1] -= money;
            return true;
        }
        return false;
    }
};