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  • Queries for Number of Palindromes(区间dp)

    You've got a string s = s1s2... s|s| of length |s|, consisting of lowercase English letters. There also are q queries, each query is described by two integers li, ri (1 ≤ li ≤ ri ≤ |s|). The answer to the query is the number of substrings of string s[li... ri], which are palindromes.

    String s[l... r] = slsl + 1... sr (1 ≤ l ≤ r ≤ |s|) is a substring of string s = s1s2... s|s|.

    String t is called a palindrome, if it reads the same from left to right and from right to left. Formally, if t = t1t2... t|t| = t|t|t|t| - 1... t1.

    Input

    The first line contains string s (1 ≤ |s| ≤ 5000). The second line contains a single integer q (1 ≤ q ≤ 106) — the number of queries. Next q lines contain the queries. The i-th of these lines contains two space-separated integers li, ri (1 ≤ li ≤ ri ≤ |s|) — the description of the i-th query.

    It is guaranteed that the given string consists only of lowercase English letters.

    Output

    Print q integers — the answers to the queries. Print the answers in the order, in which the queries are given in the input. Separate the printed numbers by whitespaces.

    Examples

    Input
    caaaba
    5
    1 1
    1 4
    2 3
    4 6
    4 5
    Output
    1
    7
    3
    4
    2

    Note

    Consider the fourth query in the first test case. String s[4... 6] = «aba». Its palindrome substrings are: «a», «b», «a», «aba».

    代码:

    #include<cstdio>
    #include<iostream>
    #include<cstring>
    #include<algorithm>
    #include<queue>
    #include<stack>
    #include<map>
    #include<set>
    #include<vector>
    #include<cmath>
    
    const int maxn=5e3+5;
    typedef long long ll;
    using namespace std;
    char str[maxn];
    
    int a[maxn][maxn],dp[maxn][maxn];
    
    int main()
    {
        scanf("%s",str+1);
        int len=strlen(str+1);
        //cout<<len<<endl;
        for(int t=1;t<=len;t++)
        {
            a[t][t]=a[t][t-1]=dp[t][t]=1;
        }
        for(int t=2;t<=len;t++)
        {
            for(int j=1;j+t-1<=len;j++)
            {
                if(str[j]==str[j+t-1]&&a[j+1][j+t-2]%2==1)
                a[j][j+t-1]=1;
                else
                {
                    a[j][j+t-1]=0;
                }
            }
        }
        for(int t=2;t<=len;t++)
        {
            for(int j=1;j+t-1<=len;j++)
            {
                dp[j][j+t-1]=dp[j][j+t-2]+dp[j+1][j+t-1]-dp[j+1][j+t-2]+a[j][j+t-1];
            }
        }
        int n;
        scanf("%d",&n);
        while(n--)
        {
            int l,r;
            scanf("%d%d",&l,&r);
            printf("%d
    ",dp[l][r]);
        }
        
        return 0;
    }
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  • 原文地址:https://www.cnblogs.com/Staceyacm/p/10826540.html
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