HDU 3613 扩展KMP

最新推荐文章于 2019-09-03 17:59:56 发布

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最新推荐文章于 2019-09-03 17:59:56 发布

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原文链接：http://www.cnblogs.com/TreeDream/p/7461813.html

本文介绍了一种使用暴力枚举和扩展KMP算法解决特定字符串匹配问题的方法，通过预处理得到匹配长度，实现快速查找回文串及最优解。

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暴力枚举大水题，判断回文，扩展KMP

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


using namespace std;

const int maxn = 500005;

int a[30];
char str[500005];
char str1[500005];
int s[500005];

int _next[maxn],_extend[maxn];
int next1[maxn],extend1[maxn];

void getnext(char *T) {
    int a = 0;
    int Tlen = strlen(T);
    _next[0] = Tlen;
    while(a<Tlen-1&&T[a]==T[a+1]) a++;
    _next[1] = a;

    a = 1;
    for(int k=2; k < Tlen; k++) {
        int p = a + _next[a] - 1,L = _next[k-a];
        if((k-1)+L>=p) {
            int j = (p-k+1) > 0 ? p - k + 1 : 0;
            while(k+j<Tlen&&T[k+j]==T[j])
                j++;
            _next[k] = j;
            a = k;
        }
        else _next[k] = L;
    }
}

void getextend(char *S,char *T) {
    int a = 0;
    getnext(T);

    int Slen = strlen(S);
    int Tlen = strlen(T);

    int Minlen = Slen < Tlen ? Slen : Tlen;
    while(a<Minlen&&S[a]==T[a]) a++;
    _extend[0] = a;
    a = 0;

    for(int k = 1; k < Slen; k++) {
        int p = a + _extend[a] - 1,L = _next[k-a];
        if((k-1)+L>=p) {
            int j = (p-k+1) > 0 ? p - k + 1 : 0;
            while(k+j<Slen&&j<Tlen&&S[k+j]==T[j]) j++;
            _extend[k] = j;
            a = k;
        }
        else
            _extend[k] = L;
    }

}


void getnext1(char *T) {
    int a = 0;
    int Tlen = strlen(T);
    next1[0] = Tlen;
    while(a<Tlen-1&&T[a]==T[a+1]) a++;
    next1[1] = a;

    a = 1;
    for(int k=2; k < Tlen; k++) {
        int p = a + next1[a] - 1,L = next1[k-a];
        if((k-1)+L>=p) {
            int j = (p-k+1) > 0 ? p - k + 1 : 0;
            while(k+j<Tlen&&T[k+j]==T[j])
                j++;
            next1[k] = j;
            a = k;
        }
        else next1[k] = L;
    }
}

void getextend1(char *S,char *T) {
    int a = 0;
    getnext1(T);

    int Slen = strlen(S);
    int Tlen = strlen(T);

    int Minlen = Slen < Tlen ? Slen : Tlen;
    while(a<Minlen&&S[a]==T[a]) a++;
    extend1[0] = a;
    a = 0;

    for(int k = 1; k < Slen; k++) {
        int p = a + extend1[a] - 1,L = next1[k-a];
        if((k-1)+L>=p) {
            int j = (p-k+1) > 0 ? p - k + 1 : 0;
            while(k+j<Slen&&j<Tlen&&S[k+j]==T[j]) j++;
            extend1[k] = j;
            a = k;
        }
        else
            extend1[k] = L;
    }

}


int main() {
    int T;
    scanf("%d",&T);
    while(T--) {

        for(int i = 0; i < 26; i++)
            scanf("%d",&a[i]);

        scanf("%s",str);

        int len = strlen(str);

        s[0] = a[ str[0] - 'a' ];
        for(int i = 1; i < len; i++)
            s[i] = s[i-1] + a[ str[i]-'a' ];

        for(int i = 0; i < len; i++)
            str1[i] = str[len-i-1];

        getextend(str1,str);
        getextend1(str,str1);

        int ans = 0;
        for(int i = 0; i < len-1; i++)
        {
            if(_extend[len-i-1]==i+1&&extend1[i+1]==len-i-1)
                ans = max(ans,s[len-1]);
            else if(_extend[len-i-1]==i+1)
                ans = max(ans,s[i]);
            else if(extend1[i+1]==len-i-1)
                ans = max(ans,s[len-1]-s[i]);
        }

        printf("%d\n",ans);
    }
    return 0;
}

转载于:https://www.cnblogs.com/TreeDream/p/7461813.html