## 题目

### 题目描述

JSZKC is going to spend his vacation!
His vacation has N days. Each day, he can choose a T-shirt to wear. Obviously, he doesn’t want to wear a singer color T-shirt since others will consider he has worn one T-shirt all the time.
To avoid this problem, he has M different T-shirt with different color. If he wears A color T-shirt this day and B color T-shirt the next day, then he will get the pleasure of fA.(notice: He is able to wear one T-shirt in two continuous days but may get a low pleasure)
Please calculate the max pleasure he can get.

### 输入

The input file contains several test cases, each of them as described below.
The first line of the input contains two integers N,M (2 ≤ N≤ 100000, 1 ≤ M≤ 100), giving the length of vacation and the T-shirts that JSZKC has.
The next follows M lines with each line M integers. The jth integer in the ith line means f[i][j](1<=f[i][j]<=1000000).
There are no more than 10 test cases.

### 输出

One line per case, an integer indicates the answer

### 样例输入

3 2
0 1
1 0
4 3
1 2 3
1 2 3
1 2 3

### 样例输出

2
9

## 题意

有n天，m件衣服，如果某一天穿了第i件衣服，第二天穿了第j件衣服，那么就会获得f[i][j]的权值。然后给你矩阵f，每件衣服可以穿无限多次，问第n天能获得的最大权值是多少。

## 思路

设$dp[t][i][j]$为第1天穿第i件衣服第t天穿第j件衣服时能获得的最大的权值。假设$a + b = t$显然有$dp[t][i][j] = max_{1 \leq k \leq m}(dp[a][i][k] + dp[b][k][j])$，考虑矩阵快速幂。

## 实现

#include <bits/stdc++.h>
const int maxn = 107;
typedef long long ll;
ll max(ll a, ll b) { return a > b ? a : b; }
int n, m;
struct Matrix {
ll data[maxn][maxn];
Matrix operator * (const Matrix &tmp) const {
Matrix ret;
memset(ret.data, 0, sizeof(ret.data));
for (int i = 1; i <= m; i++)
for (int j = 1; j <= m; j++)
for (int k = 1; k <= m; k++)
ret.data[i][j] = max(ret.data[i][j], data[i][k] + tmp.data[k][j]);
return ret;
}
} tmp;
Matrix qpow(Matrix p, int q) {
Matrix ret;
memset(ret.data, 0, sizeof(ret.data));
for (; q; q >>= 1) {
if (q & 1) ret = ret * p;
p = p * p;
}
return ret;
}
ll solve() {
Matrix result = qpow(tmp, n - 1);
ll ans = 0;
for (int i = 1; i <= m; i++)
for (int j = 1; j <= m; j++)
ans = max(ans, result.data[i][j]);
return ans;
}
int main() {
while (~scanf("%d%d", &n, &m)) {
for (int i = 1; i <= m; i++)
for (int j = 1; j <= m; j++)
scanf("%lld", tmp.data[i] + j);
printf("%lld\n", solve());
}
return 0;
}

### Comments : 2

1. 请问你的题面是从哪来的啊

1. 实在是不好意思哈，不太方便透露。:D