Evolution Game (dp idea)
Question: There is a monster that needs to evolve. Give you the number of horns and the number of eyes in each form of the monster. The horns can only evolve, and the eyes are a range. You can choose any form as the initial form, and find out how many times it can evolve at most.
Wrong idea and WA code
Looking at the data at that time, I thought that it could be traversed violently, and then the maximum value was calculated. The result was always WA. This kind of thinking will automatically select the first value that meets the conditions when it is to be forked, so that it is possible to fall into the optimal solution.
*#include <string.h>
#include <iostream>
#include <algorithm>
using namespace std;
struct node
{
int a, b;
} s[5050];
bool cmp(node c, node d)
{
return c.a < d.a;
}
int main()
{
int n, w, i, j;
cin >> n >> w;
for (i = 1; i <= n; i++)
{
cin >> s[i].a;
s[i].b = i;
}
sort(s + 1, s + n + 1, cmp);
int numm = 0;
for (j = 1; j <= n; j++)
{
int m = s[j].b, num = 0, k = s[j].a;
for (i = j + 1; i <= n; i++)
{
if (s[i].b >= m - w && s[i].b <= m + w && s[i].a > k)
{
m = s[i].b;
k = s[i].a;
num++;
}
}
if (numm < num)
numm = num;
}
cout << numm;
return 0;
}
dp code and comments
#include <bits/stdc++.h>
using namespace std;
#define maxn 5050
int h[maxn];
struct node {
int h, e;
}a[maxn];
bool cmp(node x, node y) //sort内置结构体排序函数
{
return x.h < y.h;
}
int dp[maxn];//dp数组存放每个点之前最大的进化次数
int main() {
int n, w;
cin >> n >> w;
for (int i = 1; i <= n; ++i)
{
cin >> a[i].h;
a[i].e = i;
}
sort(a + 1, a + 1 + n, cmp);//按照角的数量进行从小到大的排序
for (int i = 1; i <= n; ++i)
{
for (int j = i + 1; j <= n; ++j)
{
if (a[j].h > a[i].h && abs(a[j].e - a[i].e) <= w) //判断是否符合条件
{
dp[j] = max(dp[j], dp[i] + 1);//更新符合条件的点时最大的进化次数
}
}
}
int maxdp = 0;
for (int i = 1; i <= n; ++i)
maxdp = max(maxdp, dp[i]);//取最大值
cout << maxdp << endl;
return 0;
}