关于对ios的疑问

#include<bits/stdc++.h>
#define endl "\n"
#define ll long long
#define N 86
using namespace std;
struct node{
    double x,y;
}a[N];
int n;
double ans=2e30;
bool used[N];
inline int read();
inline void dfs(double x,double y,double sum,int cnt);
inline bool cmp(node x,node y);
inline double get_x(double x,double y,double xx,double yy);
int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);cout.tie(0);
    n=read();
    for(int i=1;i<=n;i++){
        cin>>a[i].x>>a[i].y;
    }
    sort(a+1,a+1+n,cmp);
    // dfs(0,0,0,0,0);
    dfs(0,0,0,0);
    printf("%.2lf\n",ans);
    return 0;
}
inline int read(){
    int x=0,f=1;char ch=getchar();
    while (ch<'0'||ch>'9') {if (ch=='-') f=-1;ch=getchar();}
    while (ch>='0'&&ch<='9') {x=x*10+ch-48;ch=getchar();}
    return x*f;
}
inline void dfs(double x,double y,double sum,int cnt){
    if(sum>=ans) return;
    if(cnt==n){
        ans=sum;
        return;
    }
    for(int i=1;i<=n;i++){
        if(!used[i]){
            used[i]=1;
            dfs(a[i].x,a[i].y,get_x(x,y,a[i].x,a[i].y)+sum,cnt+1);
            used[i]=0;
        }
    }
}
inline bool cmp(node x,node y){
    if(x.x!=y.x) return x.x<y.x;
    return x.y<y.y;
}
inline double get_x(double x,double y,double xx,double yy){
    return sqrt(1.0*(x-xx)*(x-xx)+1.0*(y-yy)*(y-yy));
}

#include<bits/stdc++.h>
#define endl "\n"
#define ll long long
#define N 86
using namespace std;
struct node{
    double x,y;
}a[N];
int n;
double ans=2e30;
bool used[N];
inline int read();
inline void dfs(double x,double y,double sum,int cnt);
inline bool cmp(node x,node y);
inline double get_x(double x,double y,double xx,double yy);
int main(){
    n=read();
    for(int i=1;i<=n;i++){
        cin>>a[i].x>>a[i].y;
    }
    sort(a+1,a+1+n,cmp);
    // dfs(0,0,0,0,0);
    dfs(0,0,0,0);
    printf("%.2lf\n",ans);
    return 0;
}
inline int read(){
    int x=0,f=1;char ch=getchar();
    while (ch<'0'||ch>'9') {if (ch=='-') f=-1;ch=getchar();}
    while (ch>='0'&&ch<='9') {x=x*10+ch-48;ch=getchar();}
    return x*f;
}
inline void dfs(double x,double y,double sum,int cnt){
    if(sum>=ans) return;
    if(cnt==n){
        ans=sum;
        return;
    }
    for(int i=1;i<=n;i++){
        if(!used[i]){
            used[i]=1;
            dfs(a[i].x,a[i].y,get_x(x,y,a[i].x,a[i].y)+sum,cnt+1);
            used[i]=0;
        }
    }
}
inline bool cmp(node x,node y){
    if(x.x!=y.x) return x.x<y.x;
    return x.y<y.y;
}
inline double get_x(double x,double y,double xx,double yy){
    return sqrt(1.0*(x-xx)*(x-xx)+1.0*(y-yy)*(y-yy));
}