uva 11404 dp

标签：acm   dp   uva   

UVA 11404 - Palindromic Subsequence

对于 [l, r] 区间的最长回文串，他可能是[l+1, r] 和[l, r-1]两个区间的结果。或者当s[l] == s[r]时，区间[l+1, r-1]的结果再加上以s[l], s[r]为首尾的子序列。

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

const int MAXN = 1000 + 5;

string s;
string dp[MAXN][MAXN];

void init() {
	for (int i=0; i<MAXN; i++) {
		for (int j=0; j<MAXN; j++) {
			dp[i][j] = "#";
		}
	}
}

string DP(int l, int r) {
	if (dp[l][r] != "#") return dp[l][r];
	if (l > r) return dp[l][r] = "";
	if (l == r) return dp[l][r] = string(1, s[l]);

	string a, b, c, res;

	a = DP(l+1, r);
	b = DP(l, r-1);
	c = DP(l+1, r-1);

	if (a.size() < b.size()) res = b;
	else if (a.size() > b.size()) res = a;
	else if (a < b) res = a;
	else res = b;

	if (s[l] == s[r]) {
		c = string(1, s[l]) + c + string(1, s[r]);
	}
	if (res.size() == c.size()) {
		if (res > c) res = c;
	} else if (res.size() < c.size()) res = c;

	return dp[l][r] = res;
}

int main () {
	for (; cin >> s; ) {

		init();

		string ans = DP(0, s.size()-1);

		cout << ans << endl;
	}
	return 0;
}

uva 11404 dp

标签：acm   dp   uva   

原文地址：http://blog.csdn.net/xuelanghu407/article/details/47706561