PTA甲级1103（DFS算法）

PTA甲级1103，DFS问题，采用两层vector代替不定长二维数组

#include <iostream>
#include <cmath>
#include <vector>
#include <algorithm>
using namespace std;
int powers[25];
int ans=0;
vector<int> methods;
vector<vector<int>> allmethods;
void dfs(int n,int k,int maxnum){
	if(n==0 && k==0){
		if(find(allmethods.begin(),allmethods.end(),methods)==allmethods.end()){
			int temp=0;
			for(int j=0;j<methods.size();j++)
				temp+=methods[j];
			if(ans<=temp){
				if(ans<temp)	allmethods.clear();
				allmethods.push_back(methods);
				ans=temp;
			}
		}
		return;
	}
	if(n<0 || k<0)		return;
	for(int i=maxnum;i>0;i--){
		methods.push_back(i);
		dfs(n-powers[i],k-1,i);
		methods.pop_back();
	}
}
int main(){
	int n,k,p,maxnum=1;	cin>>n>>k>>p;
	while(1){
		powers[maxnum]=pow(maxnum,p);
		if(powers[maxnum]>=n){
			break;
		}
		maxnum++;
	}
	dfs(n,k,maxnum);
	if(allmethods.empty())
		cout<<"Impossible";
	else{
		cout<<n<<" = ";
		for(int i=0;i<allmethods[0].size()-1;i++)
			cout<<allmethods[0][i]<<"^"<<p<<" + ";
		cout<<allmethods[0][allmethods[0].size()-1]<<"^"<<p;
	}
	return 0;
}