delete pics to save space

history_source/信息学奥赛一本通/2.3.3.cpp

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+#include<cstdio>
+#include<vector>
+using namespace std;
+int answer(int n)
+{
+	if(n<1) return 0;
+	if(n==1) return 1;
+	if(n==2) return 2;
+	if(n==3) return 4;
+	int a,b,c,d;
+	a=1;
+	b=2;
+	c=4;
+	d=0;
+	for(int i=4;i<=n;i++)
+	{
+		d=a+b+c;
+		a=b;
+		b=c;
+		c=d;
+	}
+	return d;
+}
+int main()
+{
+	vector<int>ans;
+	int x;
+	while(scanf("%d",&x),x!=0) ans.push_back(answer(x));
+	for(int i=0;i<ans.size();i++) printf("%d\n",ans[i]);
+	return 0;
+}