算法

===

结构体与模板

#include<iostream>
using namespace std;
struct Point{
    int x, y;
    Point(int x=0, int y=0):x(x), y(y){};
};
Point operator + (const Point &A, const Point &B){
    return Point(A.x+B.x, A.y+B.y);
}
ostream& operator << (ostream &out, const Point &p){
    out << "(" << p.x << "," << p.y << ")";
    return out;
}
template <typename T>
T sum(T *begin, T *end){
    T ans;
    for(T *i=begin; i!=end; ++i) ans = ans + *i;
    return ans;
}
int main(){
    Point a[] = {Point(1,2), Point(2,2), Point(3,3)};
    // if `Point a[] = {(), (), ()}` it can't work.
    cout << sum(a, a+2) <<endl;
    return 0;
}

STL

sort与 lower_bound

现有N个大理石，每个大理石上写了一个非负整数。首先把各数从小到大排序，然后回 答Q个问题。每个问题问是否有一个大理石写着某个整数x，如果是，还要回答哪个大理石上 写着x。排序后的大理石从左到右编号为1～N。

#include<iostream>
#include<algorithm>
using namespace std;
const int N=10000;
int a[N];
int n,q,p,x;
int main()
{
    cin>>n;
    for(int i=0;i<n;++i) cin>>a[i];
    sort(a, a+n);
    cin>>q;
    while(q--){
        cin>>x;
        p=lower_bound(a, a+n, x) - a;
        if(a[p]==x) cout<<"Found "<<x<<" at "<<p+1<<endl;
        else cout<<x<<" not found"<<endl;
    }
    return 0;
}