[BZOJ3244][NOI2013] 树的计数

感觉这个题思路很有趣的w 

这是题解w：http://www.cnblogs.com/IcyF/p/4641564.html

#include <cstdio>
#include <cstdlib>
#include <iostream>
#define MaxN 200010
using namespace std;
int n;
int d[MaxN], b[MaxN], map[MaxN], s[MaxN], da[MaxN], fl[MaxN], pos[MaxN];

void read(int &a){
    a = 0; char c = getchar();
    while (c < '0' || c > '9') c = getchar();
    while (c >= '0' && c <= '9' ) a = a*10 + c-'0', c = getchar();
}

void Read_Data(){
    read(n);
    for (int i = 1; i <= n; i++) read(d[i]);
    for (int i = 1; i <= n; i++) read(b[i]), map[b[i]] = i;
    for (int i = 1; i <= n; i++) d[i] = map[d[i]];
    for (int i = 1; i <= n; i++) pos[d[i]] = i;
}

void Solve(){
    da[1] = 1 , s[1] = 1, ++fl[1], --fl[2];
    for (int i = 1; i < n; i++) {
        if (pos[i] > pos[i+1]) da[i] = 1, ++fl[i], --fl[i+1];
        s[i] = s[i-1]+da[i];
    }
    for (int i = 1; i < n; i++) {
        if (d[i] > d[i+1]) continue;
        int t = s[d[i+1]-1] - s[d[i]-1];
        if (t) ++fl[d[i]], --fl[d[i+1]];
    }
    int flag = 0;
    double ans = 0.0;
    for (int i = 1; i < n; i++) {
        flag += fl[i];
        if (flag) ans += (double) da[i];
        else ans += 0.5;
    }
    printf("%.3f
", ans + 0.999);
    printf("%.3f
", ans + 1.000);
    printf("%.3f
", ans + 1.001);
}

int main()
{
    freopen("count.in", "r", stdin);
    freopen("count.out", "w", stdout);
    Read_Data();
    Solve();
    fclose(stdin);
    fclose(stdout);
    return 0;
}