#include <iostream>
using namespace std;
//拉格朗日插值求解方程
double * xs;   //all input x
double * ys;   //all input y
int n;      //size
//1.1275 1.1503 1.1735 1.1972
//0.1191 0.13954 0.15932 0.17903
//1.130
void init()
{
    cout << "please input n " << endl;
    cin >> n;
    xs = new double[n];
    ys = new double[n];
//input x
    cout << "please input the x‘s value !" << endl;
    for(int i=0; i<n; i++)
    {
        cin >> xs[i];
    }
//input y
    cout << "please input the y‘s value !" << endl;
    for(int i=0; i<n; i++)
    {
        cin >> ys[i];
    }
}
double everyItem(int num, double x)
{
    double y = ys[num];
    double up = 1;
    double down = 1;
    for(int i=0; i<n; i++)
    {
        if(i != num)
        {
            up *= (x - xs[i]);
            down *= (xs[num] - xs[i]);
        }
    }
    return y*up/down;
}
double lagrange(double x)
{
    double total = 0;
    for(int i=0; i<n; i++)
    {
        total = total + everyItem(i , x);
    }
    return total;
}
int main()
{
    init();
    double input;
    cout << "please input you x !" <<endl;
    cin >> input;
    double result = lagrange(input);
    cout << "the result is " << result << endl;
    return 0;
}

附件列表