UVa 10029 hash + dp

题目链接：http://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=970

第一次正式用hash表。

代码：

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;

const int maxn = 25500;
const int HASH = 1000003;

char s[maxn][20];
int head[HASH],next[maxn];
int dp[maxn];
int n;
char temp[20];   //变出来的字符串

int hash(char *s)
{
    int seed = 131;
    int ret = 0;
    while(*s)
    {
        ret = ret * seed + *(s++);
    }
    return (ret & 0x7fffffff ) % HASH ;
}

void input()
{
    n = 1;
    memset(head,-1,sizeof(head));

    while(scanf("%s",s[n]) == 1)
    {
        int id = hash(s[n]);
        next[n] = head[id];
        head[id] = n;
        n++;
    }
    n--;
}

int search()
{
    int i;
    int id = hash(temp);
    for(i=head[id]; i!=-1; i=next[i])
    {
        if(strcmp(temp,s[i]) == 0)
            break;
    }
    return i;
}

void add(int cur,int loc,int addnum)
{
    int len = strlen(s[cur]);
    int i,j;
    for(i=0,j=0; i<loc; i++)
    {
        temp[j++] = s[cur][i];
    }
    temp[j++] = 'a' + addnum;
    for(; i<len; i++)
    {
        temp[j++] = s[cur][i];
    }
    temp[j] = '';
}

void del(int cur,int loc)
{
    int len = strlen(s[cur]);
    int i,j;
    for(i=0,j=0; i<loc; i++)
        temp[j++] = s[cur][i];
    i++;
    for(; i<len; i++)
        temp[j++] = s[cur][i];
    temp[j] = '';
}

void change(int cur,int loc,int addnum)
{
    strcpy(temp,s[cur]);
    temp[loc] += addnum;
}

int dfs(int cur)
{
    if(dp[cur] != -1) return dp[cur];

    int len = strlen(s[cur]);
    int ret = 0;

    //add;
    for(int i=0; i<=len; i++)
    {
        for(int j=0; j<26; j++)
        {
            add(cur,i,j);
            int id = search();
            if(id!=-1 && strcmp(s[cur],temp) < 0)
            {
                ret = max(ret,dfs(id)+1);
            }
        }
    }

    //del;
    for(int i=0; i<len; i++)
    {
        del(cur,i);
        int id = search();
        if(id != -1 && strcmp(s[cur],temp) < 0)
            ret = max(ret,dfs(id)+1);
    }

    //change;
    for(int i=0; i<len; i++)
    {
        int lim = 'z' - s[cur][i];
        for(int j=1; j<=lim; j++)
        {
            change(cur,i,j);
            int id = search();
            if(id != -1 && strcmp(s[cur],temp) < 0)
                ret = max(ret,dfs(id)+1);
        }
    }
    dp[cur] = ret;
    return ret;
}


void solve()
{
    memset(dp,-1,sizeof(dp));
    int ans = 0;
    for(int i=1; i<=n; i++)
    {
        ans = max(ans,dfs(i));
    }
    printf("%d
",ans+1);
}
int main()
{
   // freopen("E:\acm\input.txt","r",stdin);
    input();
    solve();
}