POJ 1179 Polygon

区间DP

拆链成环,然后区间DP即可,注意初始化,以及每个地方都要遍历到

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cmath>
#define inf 0x3f3f
using namespace std;
int num[205], dp[205][205][2], n;
char opt[205];
int main() {
	cin >> n;
	for(int i = 1; i <= 2 * n; i++) {
		for(int j = 1; j <= 2 * n; j++) 
			dp[i][j][1] = -inf, dp[i][j][0] = inf;
	}
	for(int i = 1; i <= n; i++) {
		scanf(" %c ", &opt[i]);
		opt[i + n] = opt[i];
		cin >> num[i];
		num[i + n] = num[i];
		dp[i][i][0] = dp[i][i][1] = num[i];
		dp[i + n][i + n][0] = dp[i + n][i + n][1] = num[i];
	}
	for(int k = 2; k <= n; k++) {
		for(int i = 1; i + k - 1 <= 2 * n; i++) {
			int j = i + k - 1;
			for(int t = i; t < j; t++) {
				if(opt[t + 1] == 'x') {
					dp[i][j][1] = max(dp[i][j][1], dp[i][t][1] * dp[t + 1][j][1]);
					dp[i][j][1] = max(dp[i][j][1], dp[i][t][0] * dp[t + 1][j][0]);
					dp[i][j][0] = min(dp[i][j][0], dp[i][t][0] * dp[t + 1][j][0]);
					dp[i][j][0] = min(dp[i][j][0], dp[i][t][1] * dp[t + 1][j][0]);
					dp[i][j][0] = min(dp[i][j][0], dp[i][t][0] * dp[t + 1][j][1]);
				}else {
					dp[i][j][1] = max(dp[i][j][1], dp[i][t][1] + dp[t + 1][j][1]);
					dp[i][j][0] = min(dp[i][j][0], dp[i][t][0] + dp[t + 1][j][0]);
				}
			}
		}
	}
	int ans = 0;
	/*for(int k = 1; k <= n; k++) {
		for(int i = 1; i + k - 1 <=  2 * n; i++) {
			int j = i + k - 1;
			printf("%d ", dp[i][j][1]);
		}
		printf("\n");
	}
	printf("\n");*/
	for(int i = 1; i <= n; i++) {
		ans = max(ans, dp[i][i + n - 1][1]);
	}
	cout << ans << endl;
	for(int i = 1; i <= n; i++) {
		if(ans == dp[i][i + n - 1][1]) cout << i << " ";
	}
	cout << endl;
	return 0;
}