CF1312E Array Shrinking

题目链接：https://codeforces.com/contest/1312

 

题目大意：

 

 

 

想法：

考虑区间DP

我们定义 f(i,j) 代表区间 i 到 j 的最小长度，w(i,j) 代表 区间 i 到 j的数字

转移方程也很容易想到

当 f(i,k) = f(k+1,j)  = 1 && w(i,k) = w(k+1,j)             f(i,j) = 1 ,w(i,j) = w(i,k) + 1

#pragma GCC optimize(3,"Ofast","inline")//O3优化
#pragma GCC optimize(2)//O2优化
#include <algorithm>
#include <string>
#include <string.h>
#include <vector>
#include <map>
#include <stack>
#include <set>
#include <queue>
#include <math.h>
#include <cstdio>
#include <iomanip>
#include <time.h>
#include <bitset>
#include <cmath>
#include <sstream>
#include <iostream>
#include <cstring>

#define LL long long
#define ls nod<<1
#define rs (nod<<1)+1
#define pii pair<int,int>
#define mp make_pair
#define pb push_back
#define INF 0x3f3f3f3f
#define max(a,b) (a>b?a:b)
#define min(a,b) (a<b?a:b)

const double eps = 1e-10;
const int maxn = 500 + 10;
const LL mod = 998244353;

int sgn(double a){return a < -eps ? -1 : a < eps ? 0 : 1;}
using namespace std;

int f[maxn][maxn];
int w[maxn][maxn];

int main() {
    ios::sync_with_stdio(0);
    memset(f,INF, sizeof(f));
    int n;
    cin >> n;
    for (int i = 1;i <= n;i++) {
        f[i][i] = 1;
        cin >> w[i][i];
    }
    for (int l = 2;l <= n;l++) {
        for (int i = 1;l+i-1 <= n;i++) {
            int j = l + i - 1;
            for (int k = i;k <= j;k++) {
                f[i][j] = min(f[i][j],f[i][k]+f[k+1][j]);
                if (w[i][k] == w[k+1][j] && f[i][k] == f[k+1][j] && f[i][k] == 1) {
                    f[i][j] = 1;
                    w[i][j] = w[i][k] + 1;
                }
            }
        }
    }
    cout << f[1][n] << endl;
    return 0;
}