union Data{
    int num;    
    float value;    
    char symbol;
};
union Data data;

struct Node {
    int data;    
    Node* next;
};

现在有一个指向链表头部的指针：Node* head。如果想要在链表中插入一个新节点，其成员data的值为42，并使新节点成为链表的第一个节点，下面哪个操作是正确的？（ ）

#include<iostream>
#include<cmath>
using namespace std;

double f(double a,double b,double c){
    double s=(a+b+c)/2;
    return sqrt(s*(s-a)*(s-b)*(s-c));
}

int main(){
   cout.flags(ios::fixed);
   cout.precision(4);
   
   int a,b,c;
   cin>>a>>b>>c;
   cout<<f(a,b,c)<<endl;
   return 0;
}

#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
 
int f(string x,string y){
    int m=x.size();
    int n=y.size();
    vector<vector<int>>v(m+1,vector<int>(n+1,0));
   for(int i=1;i<=m;i++){
       for(int j=1;j<=n;j++){
            if(x[i-1]==y[j-1]){
                v[i][j]=v[i-1][j-1]+1;
            }else{
                v[i][j]=max(v[i-1][j],v[i][j-1]);
            }
        }
    }
    return v[m][n];
}

bool g(string x,string y){
    if(x.size() != y.size()){
        return false;
    }
    return f(x+x,y)==y.size();
}

int main(){
    string x,y;
    cin>>x>>y;
    cout<<g(x,y)<<endl;
    return 0;
}

#include <iostream>
#include <vector>

using namespace std;

int find_missing(vector<int>& nums){
	int left = 0, right = nums.size() - 1;
	while (left < right){
  		int mid = left + (right-left) / 2;
  		if (nums[mid]==mid+ ①){
       		②;
   		}else{
     		③
   		}
  	}
 	return ④;
}

int main(){
	int n;
	cin >> n;
	vector<int> nums(n);
	for (int i= 0; i< n; i++) cin >> nums[i];
	int missing_number = find_missing(nums);
	if(missing_number == ⑤) {
    		cout << "Sequence is consecutive" << endl;
	}else{
   		cout << "Missing number is " << missing numbeer << endl;
	}
	return 0;
}