POJ 1179 Polygon

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题目大意：给一个多边形，每个顶点有一个值，每个边编号从1到N，边的属性是加或者乘。首先先拆掉一条边，剩下的如下做：选定一条边以及这条边的两个端点（两个数）用新顶点替换（新顶点即：按照这条边的属性（加或乘）算出这两个数的乘积或者和）。到最后剩一个点，也就是一个值。求这些值的最大值输出，并输出此时最先拆掉的是哪条边。

Input:

4

t  -7  t  4  x  2  x  5

Output:

33

1 2

区间DP问题

注意最大值可以由两个最小值相乘得到

注意下标和求min_v和max_v时的逻辑简化

#include <iostream>
#include <vector>
using namespace std;

#define SIZE 70
#define MAX_V 0
#define MIN_V 1
#define INF 1 << 15

int dp[SIZE][SIZE][2];
char symbols[SIZE];
int node_values[SIZE];
int node_num;
vector< int > v;

int cal( int head, int tail, char symbol ){
    if( symbol == ‘t‘ )
        return head + tail;
    else
        return head * tail;
}

int main(){
    cin >> node_num;
    for( int i = 0; i < node_num; ++i ){
        cin >> symbols[i] >> node_values[i];
    }

    for( int i = 0; i < node_num; ++i )
        for( int j = 0; j < node_num; ++j )
            if( i == j )
                dp[i][i][MAX_V] = dp[i][i][MIN_V] = node_values[i];

    for( int len = 1; len <= node_num - 1; ++len ){
        for( int from = 0; from < node_num; ++from ){
            int to = ( from + len ) % node_num;
            int min_v = INF;
            int max_v = -INF;
            for( int count_ = 0; count_ < len; ++count_ ){
                int cut = ( from + count_ ) % node_num;
                int cut1 = ( from + count_ + 1 ) % node_num;
                int temp = 0;
                temp = cal( dp[from][cut][MAX_V], dp[cut1][to][MAX_V], symbols[cut1] );
                max_v = max( temp, max_v );
                temp = cal( dp[from][cut][MIN_V], dp[cut1][to][MIN_V], symbols[cut1] );
                max_v = max( temp, max_v );
                temp = cal( dp[from][cut][MIN_V], dp[cut1][to][MAX_V], symbols[cut1] );
                min_v = min( temp, min_v );
                temp = cal( dp[from][cut][MAX_V], dp[cut1][to][MIN_V], symbols[cut1] );
                min_v = min( temp, min_v );
            }
            dp[from][to][MAX_V] = max_v;
            dp[from][to][MIN_V] = min_v;
        }
    }
    int temp = -INF;
    for( int from = 0; from < node_num; ++from ){
        int to = ( from + node_num - 1 ) % node_num;
        if( dp[from][to][MAX_V] > temp ){
                temp = dp[from][to][MAX_V];
                v.clear();
                v.push_back( from );
        }
        else if( dp[from][to][MAX_V] == temp )
            v.push_back( from );
    }
    cout << temp <<endl;
    for( int i = 0; i < v.size(); ++i )
        cout << v[i] + 1 << " ";
    cout << endl;
    return 0;
}

POJ 1179 Polygon,布布扣,bubuko.com

POJ 1179 Polygon

标签：style   blog   class   c   code   ext   

原文地址：http://blog.csdn.net/pandora_madara/article/details/26348483