UVA - 1374 Power Calculus

题目大意：给出 n，问说至少计算几步得到 x^n。

解题思路：迭代深搜，枚举步数，然后深搜判断是否可行。需要优化，当当前数 now 按照最大方案执行后仍然小于 n，则说明不可行。

#include <cstdio>
int n, MAX, A[35];

bool DFS(int cur, int now){
    if (cur > MAX || now <= 0 || now << (MAX - cur) < n)
        return false;
    if (now == n || now << (MAX - cur) == n)
        return true;

    A[cur] = now;
    for (int i = 0; i <= cur; ++i) {
        if (DFS(cur + 1, now + A[i]))
            return true;
        if (DFS(cur + 1, now - A[i]))
            return true;
    }

    return false;
}

int main() {
    while (scanf("%d", &n), n) {
        for (MAX = 0; !DFS(0, 1); ++MAX);
        printf("%d\n", MAX);
    }
    return 0;
}