leetcode(c++)(区间DP)

#include <iostream>
#include <vector>
#include <string>

using namespace std;

string longestPalindrome(string s)
{
    int n = s.size();
    vector<vector<bool>>dp(n,vector<bool>(n));
    int start = 0, end = 0;
    for(int i = n - 1; i >= 0; --i)
    {
        for(int j = i; j < n; ++j)
        {
            if(s[i] == s[j] && (j - i < 2 || dp[i+1][j-1]))
            {
                if(end - start < (j - i))
                {
                    start = i;
                    end = j;
                }
                dp[i][j] = true;
            }
        }
    }
    return s.substr(start,end-start+1);
}

int dfs(string s,int i,int j, vector<vector<int>>&memo)
{
    if(i > j) return 0;
    if(i == j) return 1;
    if(memo[i][j] != -1)return memo[i][j];
    if(s[i] == s[j])memo[i][j] = dfs(s,i+1,j-1,memo) + 2;
    else memo[i][j] = max(dfs(s,i+1,j,memo),dfs(s,i,j-1,memo));
    return memo[i][j];
}

int longestPalindromeSubseq(string s)
{
    int n = s.size();
    vector<vector<int>>memo(n,vector<int>(n,-1));
    return dfs(s,0,n-1,memo);
}

int longestPalindromeSubseqII(string s)
{
    int n = s.size();
    vector<vector<int>>dp(n,vector<int>(n));
    for(int i = n - 1; i >= 0; --i)
    {
        dp[i][i] = 1;
        for(int j = i + 1; j < n; ++j)
        {
            if(s[i] == s[j])dp[i][j] = dp[i + 1][j-1] + 2;
            else dp[i][j] = max(dp[i][j-1],dp[i+1][j]);
        }    
    }
    return dp[0][n-1];
}

int lcs(string r, string s)
{
    int m = r.size();
    int n = s.size();
    vector<vector<int>>dp(m+1,vector<int>(n+1,0));
    for(int i = 0; i < m; ++i)
    {
        for(int j = 0; j < n; ++j)
        {
            if(r[i] == s[j])
            {
                dp[i+1][j+1] = dp[i][j] + 1;
            }        
            else
            {
                dp[i+1][j+1] = max(dp[i+1][j],dp[i][j+1]);
            }
        }
    }
    return dp[n][n];
    
}

bool isValidPalindrome(string s, int k)
{
    string r = s;
    reverse(s.begin(),s.end());       
    return (r.size() - lcs(r,s)) <= k;
}

int main()
{
    //LeetCode5
    string s = "babad";
    cout << longestPalindrome(s) << endl;

    //LeetCode516
    s = "bbbab";
    cout << longestPalindromeSubseq(s) << endl;
    cout << longestPalindromeSubseqII(s) << endl;

    //LeetCode1216
    s = "abcdeca";
    int k = 2;
    cout << isValidPalindrome(s,k) << endl;
    return 0;
}