AcWing 793. 高精度乘法

# 高精度乘法

#include <iostream>
#include <vector>

using namespace std;

vector<int> mul(vector<int> &A, int b){
	vector<int> C;
	int t = 0;
	for(int i = 0; i < A.size() || t; i++){
		if(i < A.size()) t += A[i] * b;
		C.push_back(t % 10);
		t /= 10;
	}
	while(C.size() > 1 && C.back() == 0) C.pop_back();
	return C;
}
int main(){
	string a;
	int b;
	cin >> a >> b;
	vector<int> A;
	for(int i = a.size() - 1; i >= 0; i--) A.push_back(a[i] - '0');
	auto C = mul(A, b);
	for(int i = C.size() - 1; i >= 0; i--) printf("%d", C[i]);
	return 0;
}

#include <iostream>
#include <vector>

using namespace std;

vector<int> mul(vector<int> &A, int b){
    vector<int> C;
    
    int t = 0;
    
    for(int i = 0; i < A.size() || t; i++){
        if (i < A.size()) t += A[i] * b;
        C.push_back(t % 10);
        t /= 10;
    }
    
    while (C.size() > 1 && C.back() == 0) C.pop_back(); 
    //去前导0
    
    return C;
}

int main(){
    string a;
    int b;
    
    cin >> a >> b;
    
    vector<int> A;
    for(int i = a.size() - 1; i >= 0; i--) A.push_back(a[i] - '0');
    //a[i] - '0' 为隐式转化 将字符类型的数字转换成整数类型数字
    
    auto C = mul(A, b);
    
    for(int i = C.size() - 1; i >= 0; i--) printf("%d", C[i]);
    
    return 0;
}