浙大 PAT 甲级 1103 Integer Factorization DFS+剪枝

这题的超时弄得我要崩溃了…各种细节处的剪枝，不停剪了很多地方，依然超时。最后用整型数组代替了vector，通过。血泪教训，第二次了，超时的时候把vector换成原生数组会快好几倍。

#include<stdio.h>
#include<vector>
#include<math.h>
#include<memory.h>
using namespace std;

vector<int> addend;
int bestans[405];
int bestmax;
int bestsum;

int N, K, P;

void DFS(int res, int* ans, int sum, int start,int layer)
{
    if (layer >= K) return;
    for (int i = start; i >= 0; i--)
    {
        res += addend[i];
        if (res <= N)
        {
            ans[layer] = i + 1;
            layer++;
            sum += (i + 1);
            if (layer == K && res == N)
            {
                if (sum > bestsum || (sum == bestsum&&ans[0] > bestans[0]))
                {
                    bestsum = sum;
                    memcpy(bestans, ans, sizeof(int)*K);
                }
                break;
            }
            else if (layer < K && res < N)
            {
                DFS(res, ans, sum, i,layer);
            }
            layer--;
            sum -= (i + 1);
        }
        res -= addend[i];
    }
}

void init()
{
    for (int i = 1; i <= N; i++)
    {
        int add = pow((double)i, P);
        if (add > N) break;
        else addend.push_back(add);
    }
}

int main()
{
    scanf("%d %d %d", &N, &K, &P);
    bestsum = -1;
    init();
    int ans[405];
    DFS(0, ans, 0, addend.size() - 1, 0);
    if (bestsum == -1)
    {
        printf("Impossible\n");
    }
    else
    {
        printf("%d = ", N);
        for (int i = 0; i < K; i++)
        {
            if (i == K - 1)
            {
                printf("%d^%d\n", bestans[i], P);
            }
            else
            {
                printf("%d^%d + ", bestans[i], P);
            }
        }
    }
    return 0;
}

标签：剪枝,layer,PAT,addend,int,res,bestsum,Factorization,ans
来源： https://blog.csdn.net/qq_39115541/article/details/100518232