uva 10029 HASH + DP

来源：互联网发布：理解信息与数据编辑：程序博客网时间：2024/05/16 09:30
题意：
给一个字典，里面有好多单词。单词可以由增加、删除、变换，变成另一个单词，问能变换的最长单词长度。
解析：
HASH+dp
代码：
#include <iostream>#include <cstdio>#include <cstdlib>#include <algorithm>#include <cstring>#include <cmath>#include <stack>#include <vector>#include <queue>#include <map>#include <climits>#include <cassert>#define LL long longusing namespace std;const int inf = 0x3f3f3f3f;const double eps = 1e-8;const double pi = 4 * atan(1.0);const double ee = exp(1.0);const int maxn = 25000 + 10;const int HASH = 1000003;int n;int head[HASH], next[maxn];char s[maxn][20], t[20];int dp[maxn];//hash ...int Hash(char str[]){    int v = 0, seed = 88;    while (*str)        v = v * seed + *(str++);    return (v & 0x7fffffff) % HASH;}void Insert(int x){    int h = Hash(s[x]);    next[x] = head[h];    head[h] = x;}int Search(){    int i;    int h = Hash(t);//    for (i = head[h]; i != -1; i = next[i])    {        if (strcmp(t, s[i]) == 0)        {            break;        }    }    return i;}//dp ...void add(char str[], int pos, int key){    memset(t, 0, sizeof(t));    int i, j;    for (i = 0, j = 0; i < pos; i++, j++)    {        t[j] = str[i];    }    t[j++] = 'a' + key;    for (; str[i]; i++, j++)    {        t[j] = str[i];    }    t[j] = '\0';}void del(char str[], int pos){    memset(t, 0, sizeof(t));    int i, j;    for (i = 0, j = 0; i < pos; i++, j++)    {        t[j] = str[i];    }    i++;    for (; str[i]; i++, j++)    {        t[j] = str[i];    }    t[j] = '\0';}void change(char str[], int pos, int key){    memset(t, 0, sizeof(t));    strcpy(t, str);    t[pos] = 'a' + key;}int Dfs(int cur){    if (dp[cur] != -1)        return dp[cur];    int res = 0;    int len = strlen(s[cur]);    //add    for (int i = 0; i <= len; i++)    {        for (int k = 0; k < 26; k++)        {            add(s[cur], i, k);            int pos = Search();            if (pos != -1 && strcmp(s[cur], t) < 0)            {                int t = Dfs(pos) + 1;///pos                if (res < t)                {                    res = t;                }            }        }    }    //delete    for (int i = 0; i < len; i++)    {        del(s[cur], i);        int pos = Search();        if (pos != -1 && strcmp(s[cur], t) < 0)        {            int t = Dfs(pos) + 1;///pos            if (res < t)            {                res = t;            }        }    }    //change    for (int i = 0; i < len; i++)    {        for (int k = 0; k < 26; k++)        {            change(s[cur], i, k);            int pos = Search();            if (pos != -1 && strcmp(s[cur], t) < 0)            {                int t = Dfs(pos) + 1;///pos                if (res < t)                {                    res = t;                }            }        }    }    return dp[cur] = res;}int main(){#ifdef LOCAL    freopen("in.txt", "r", stdin);#endif // LOCAL    n = 0;    memset(head, -1, sizeof(head));    while (scanf("%s", s[n]) != EOF)    {        Insert(n);        n++;    }    memset(dp, -1, sizeof(dp));    int ans = 0;    for (int i = 0; i < n; i++)    {        int t = Dfs(i) + 1;        if (ans < t)        {            ans = t;        }    }    printf("%d\n", ans);    return 0;}
0 0