PAT A1103

题目：https://pintia.cn/problem-sets/994805342720868352/problems/994805364711604224

我真的是蠢到爆了，我想着输出时需要从大到小，而大在前，小在后，就用队列来输出，于是把答案往队列queue中存。忽略了致命的错误，pop的时候，是最前面的被pop而不是选不选当前index。所以只能用vector。

#include <cstdio>
#include <cmath>
#include <queue>
using namespace std;
queue<int> temp, ans;
int n, k, p, maxsum;
void DFS(int index, int nowK, int x, int sum){
	if(index == 0 || x > n || nowK > k)
		return;
	if(nowK == k && x == n){
		if(ans.empty() || sum > maxsum){
			ans = temp;
			maxsum = sum;
		}
		return;
	}
	temp.push(index);
	DFS(index, nowK + 1, x + pow((double)index, (double)p), sum + index);
	temp.pop();
	DFS(index - 1, nowK, x , sum);
}
int main(){
	scanf("%d%d%d", &n, &k, &p);
	int j = pow((double)n, 1.0 / p);
	DFS( j, 0, 0, 0);
	if(!ans.empty()){
		printf("%d =", n);
		for(int i = 0; i < k; i++){
			printf(" %d^%d", ans.front(), p);
			ans.pop();
			if(i < k - 1)
				printf(" +");
		}
		printf("\n");
	}
	else
		printf("Impossible\n");
	return 0;
}

修正后：

#include <cstdio>
#include <cmath>
#include <vector>
using namespace std;
vector<int> temp, ans;
int n, k, p, maxsum;
void DFS(int index, int nowK, int x, int sum){
	if(index == 0 || x > n || nowK > k)
		return;
	if(nowK == k && x == n){
		if(ans.empty() || sum > maxsum){
			ans = temp;
			maxsum = sum;
		}
		return;
	}
	temp.push_back(index);
	DFS(index, nowK + 1, x + pow((double)index, (double)p), sum + index);
	temp.pop_back();
	DFS(index - 1, nowK, x , sum);
}
int main(){
	scanf("%d%d%d", &n, &k, &p);
	int j = pow((double)n, 1.0 / p);
	DFS( j, 0, 0, 0);
	if(!ans.empty()){
		printf("%d =", n);
		for(int i = 0; i < k; i++){
			printf(" %d^%d", ans[i], p);
			if(i < k - 1)
				printf(" +");
		}
		printf("\n");
	}
	else
		printf("Impossible\n");
	return 0;
}