UPC 2959: Caoshen like math 这就是个水题

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <cstdlib>
#include <map>
#include <stack>
#include <queue>
#include <vector>
 
const int MAXN = 1000000 + 10;
const double ESP = 10e-8;
const double Pi = atan(1.0) * 4;
const int INF = 0x7fffffff;
const int MOD = 2012;
typedef long long LL;
 
LL gcd(LL a,LL b){
    return b ?gcd(b,a%b): a;
}
using namespace std;
struct P{
    int x;
    int pp;
    bool operator < (const P a)const{
        return x < a.x;
    }
};
int a[MAXN];
P b[MAXN];
int main(){
//    freopen("input.txt","r",stdin);
    int n;
    while(~scanf("%d",&n)){
        for(int i = 0;i < n;i++){
            scanf("%d",&a[i]);
            b[i].x = a[i];
            b[i].pp = i;
        }
        sort(b,b+n);
        int ans = 0;
        for(int i = 0;i < n;i++){
            if(a[i] != b[i].x){
                int pp = b[i].pp;
                int tmp = a[i];
                a[i] = b[i].x;
                a[pp] = tmp;
                P xx;
                xx.x = tmp;
                int x = lower_bound(b,b+n,xx) - b;
                b[x].pp = pp;
                ans++;
            }
        }
        printf("%d\n",ans);
    }
    return 0;
}