POJ 2955 Brackets 區間DP

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題目來源：POJ 2955 Brackets

題意：最括號對稱

思路：

#include <cstdio>#include <cstring>#include <algorithm>#include <cstdlib>using namespace std;const int maxn = 210;int dp[maxn][maxn];char a[maxn];int b[maxn];int dfs(int l, int r){if(l > r)return 0;if(dp[l][r] != -1)return dp[l][r];if(l+1 == r){if(b[l] < 2 && b[l]+b[r] == 3)dp[l][r] = 1;elsedp[l][r] = 0;return dp[l][r];}if(l == r){dp[l][r] = 0;return dp[l][r];}dp[l][r] = 0;if(b[l] < 2 && b[l] + b[r] == 3){dp[l][r] = max(dp[l][r], dfs(l+1, r-1)+1);}else {dp[l][r] = max(dp[l][r], dfs(l+1, r-1));}for(int i = l; i <= r; i++){dp[l][r] = max(dp[l][r], dfs(l, i)+dfs(i+1, r));}return dp[l][r];}int main(){while(gets(a) && (strcmp(a, "end"))){memset(dp, -1, sizeof(dp));for(int i = 0; a[i]; i++){if(a[i] == '(')b[i] = 0;else if(a[i] == ')')b[i] = 3;else if(a[i] == '[')b[i] = 1;else if(a[i] == ']')b[i] = 2;}printf("%d\n", dfs(0, strlen(a)-1)*2);}return 0;}