UVa 1374 - Power Calculus <IDA*算法>

本题值得学习的地方就是乐观估计函数的推到，需要数学指数的运算，另外计算2的n次方的时候可以用1<<n来快速计算，值得学习。

另外对于当前的集合存储，用C数列存储再合适不过了，刚开始用set来存，对数据进行增删浪费了大量时间，而且操作起来特别麻烦。

#include <bits/stdc++.h>using namespace std;int n, maxd, res[32];bool DFS(int d){    if(d == maxd) return res[d-1]==n;    if(*max_element(res, res+d) * (1<<(maxd-d)) < n) return false;    for(int i = d-1; i >= 0; --i){        int v1 = res[d-1] + res[i], v2 = abs(res[d-1] - res[i]);        if(!count(res, res+d, v1)){            res[d] = v1;            if(DFS(d+1)) return true;        }        if(!count(res, res+d, v2)){            res[d] = v2;            if(DFS(d+1)) return true;        }    }    return false;}int main(){    while(res[0] = 1, maxd = 1, scanf("%d", &n), n){        while(!DFS(1))            maxd++;        printf("%d\n", maxd - 1);    }return 0;}

打表的方法，只用了9ms

#include <stdio.h>int res[1024] = {0, 0, 1, 2, 2, 3, 3, 4, 3, 4, 4, 5, 4, 5, 5, 5, 4, 5, 5, 6, 5, 6, 6, 6, 5, 6, 6, 6, 6, 7, 6, 6, 5, 6, 6, 7, 6, 7, 7, 7, 6, 7, 7, 7, 7, 7, 7, 7, 6, 7, 7, 7, 7, 8, 7, 8, 7, 8, 8, 8, 7, 8, 7, 7, 6, 7, 7, 8, 7, 8, 8, 8, 7, 8, 8, 8, 8, 8, 8, 8, 7, 8, 8, 8, 8, 8, 8, 9, 8, 9, 8, 9, 8, 8, 8, 8, 7, 8, 8, 8, 8, 9, 8, 9, 8, 9, 9, 9, 8, 9, 9, 9, 8, 9, 9, 9, 9, 9, 9, 9, 8, 9, 9, 9, 8, 9, 8, 8, 7, 8, 8, 9, 8, 9, 9, 9, 8, 9, 9, 9, 9, 9, 9, 9, 8, 9, 9, 9, 9, 9, 9, 10, 9, 9, 9, 9, 9, 9, 9, 9, 8, 9, 9, 9, 9, 9, 9, 10, 9, 10, 9, 10, 9, 10, 10, 10, 9, 10, 10, 10, 9, 10, 10, 10, 9, 10, 9, 10, 9, 9, 9, 9, 8, 9, 9, 9, 9, 10, 9, 10, 9, 10, 10, 10, 9, 10, 10, 10, 9, 10, 10, 10, 10, 10, 10, 10, 9, 10, 10, 10, 10, 10, 10, 10, 9, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 9, 10, 10, 10, 10, 10, 10, 10, 9, 10, 10, 10, 9, 10, 9, 9, 8, 9, 9, 10, 9, 10, 10, 10, 9, 10, 10, 11, 10, 11, 10, 10, 9, 10, 10, 11, 10, 11, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 9, 10, 10, 10, 10, 10, 10, 11, 10, 10, 10, 11, 10, 11, 11, 11, 10, 11, 10, 11, 10, 11, 10, 11, 10, 11, 10, 10, 10, 10, 10, 10, 9, 10, 10, 10, 10, 10, 10, 11, 10, 11, 10, 11, 10, 11, 11, 11, 10, 11, 11, 11, 10, 11, 11, 11, 10, 11, 11, 11, 11, 11, 11, 11, 10, 11, 11, 11, 11, 11, 11, 11, 10, 11, 11, 11, 11, 11, 11, 11, 10, 11, 11, 11, 10, 11, 11, 11, 10, 11, 10, 11, 10, 10, 10, 10, 9, 10, 10, 10, 10, 11, 10, 11, 10, 11, 11, 11, 10, 11, 11, 11, 10, 11, 11, 11, 11, 11, 11, 11, 10, 11, 11, 11, 11, 11, 11, 11, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 12, 11, 12, 11, 11, 11, 12, 11, 12, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 12, 11, 12, 11, 11, 10, 11, 11, 12, 11, 12, 11, 11, 10, 11, 11, 11, 10, 11, 10, 10, 9, 10, 10, 11, 10, 11, 11, 11, 10, 11, 11, 12, 11, 12, 11, 11, 10, 11, 11, 12, 11, 12, 12, 11, 11, 12, 12, 12, 11, 12, 11, 11, 10, 11, 11, 12, 11, 12, 12, 12, 11, 11, 12, 12, 11, 12, 11, 12, 11, 11, 11, 12, 11, 12, 11, 11, 11, 12, 11, 11, 11, 11, 11, 11, 10, 11, 11, 11, 11, 11, 11, 12, 11, 11, 11, 12, 11, 12, 12, 12, 11, 12, 11, 12, 11, 12, 12, 12, 11, 12, 12, 12, 12, 12, 12, 12, 11, 12, 12, 12, 11, 12, 12, 12, 11, 12, 12, 12, 11, 12, 12, 12, 11, 12, 12, 12, 11, 12, 11, 12, 11, 12, 11, 11, 11, 11, 11, 11, 10, 11, 11, 11, 11, 11, 11, 12, 11, 12, 11, 12, 11, 12, 12, 12, 11, 12, 12, 12, 11, 12, 12, 12, 11, 12, 12, 12, 12, 12, 12, 12, 11, 12, 12, 12, 12, 12, 12, 12, 11, 12, 12, 12, 12, 12, 12, 12, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 11, 12, 12, 12, 12, 12, 12, 12, 11, 12, 12, 12, 12, 12, 12, 12, 11, 12, 12, 12, 11, 12, 12, 12, 11, 12, 11, 12, 11, 11, 11, 11, 10, 11, 11, 11, 11, 12, 11, 12, 11, 12, 12, 12, 11, 12, 12, 12, 11, 12, 12, 12, 12, 12, 12, 12, 11, 12, 12, 12, 12, 12, 12, 12, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 13, 12, 12, 12, 12, 11, 12, 12, 12, 12, 13, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 13, 12, 12, 12, 13, 12, 13, 12, 12, 12, 13, 12, 12, 12, 12, 12, 12, 11, 12, 12, 12, 12, 12, 12, 13, 12, 12, 12, 13, 12, 13, 12, 12, 12, 13, 12, 13, 12, 13, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 13, 12, 13, 12, 13, 12, 13, 12, 13, 12, 13, 12, 13, 12, 13, 13, 13, 12, 13, 13, 13, 12, 13, 12, 13, 12, 13, 13, 13, 12, 13, 13, 13, 12, 13, 12, 13, 12, 12, 12, 13, 12, 13, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 13, 12, 13, 12, 12, 12, 12, 12, 13, 12, 13, 13, 13, 12, 13, 13, 13, 12, 13, 12, 12, 11, 12, 12, 13, 12, 13, 13, 13, 12};int main(){    int n;    while(scanf("%d", &n), n)        printf("%d\n", res[n]);    return 0;}