zoj 1876 Edit Step Ladders
An edit step is a transformation from one word x to another word y
such that x and y are words in the dictionary, and x can be
transformed to y by adding, deleting, or changing one letter. So
the transformation from dig to dog or from dog to do are both edit
steps. An edit step ladder is a lexicographically ordered sequence
of words w1, w2, ... wn such that the transformation from wi to wi+1
is an edit step for all i from 1 to n-1.
For a given dictionary, you are to compute the length of the
longest edit step ladder.
Input
The input to your program consists of the dictionary - a set of lower case words in lexicographic order - one per line (the character "-" or "'" may also appear). No word exceeds 16 letters and there are no more than 25000 words in the dictionary.
Output
The output consists of a single integer, the number of words in the longest edit step ladder.
Sample Input
cat
dig
dog
fig
fin
fine
fog
log
wine
Sample Output
5
-
#include <iostream> #include <cstdio> #include <cstring> #include <algorithm> using namespace std; const int MAXN = 25010; const int HASH = 1000010; int n,head[HASH],next[MAXN],f[MAXN]; char b[MAXN][20],temp[20]; int hash(char *s){ int v = 0,seed = 131; while (*s) v = v * seed + *(s++); return (v & 0x7fffffff) % HASH; } void insert(int s){ int h = hash(b[s]); next[s] = head[h]; head[h] = s; } int search(char *s){ int i,h = hash(s); for (i = head[h]; i != -1; i = next[i]) if (!strcmp(b[i],s)) break; return i; } void add(char *s, int p, int d){ int i = 0, j = 0; while (i < p) temp[j++] = s[i++]; temp[j++] = 'a' + d; while (s[i]) temp[j++] = s[i++]; temp[j] = '\0'; } void del(char *s, int p){ int i = 0,j = 0; while (i < p) temp[j++] = s[i++]; i++; while (s[i]) temp[j++] = s[i++]; temp[j] = '\0'; } void change(char *s, int p, int d){ strcpy(temp, s); temp[p] = 'a' + d; } int dp(int s){ if (f[s] != -1) return f[s]; int ans = 0; int len = strlen(b[s]); for (int p = 0; p <= len; p++) for (int d = 0; d < 26; d++){ add(b[s], p, d); int v = search(temp); if (v != -1 && strcmp(b[s], temp) < 0){ int t = dp(v); if (ans < t+1) ans = t+1; } } for (int p = 0; p < len; p++){ del(b[s], p); int v = search(temp); if (v != -1 && strcmp(b[s], temp) < 0){ int t = dp(v); if (ans < t+1) ans = t+1; } } for (int p = 0; p < len; p++) for (int d = 0; d < 26; d++){ change(b[s], p, d); int v = search(temp); if (v != -1 && strcmp(b[s], temp) < 0){ int t = dp(v); if (ans < t+1) ans = t+1; } } return f[s] = ans; } int main(){ n = 0; memset(head, -1, sizeof(head)); while (scanf("%s", b[n]) != EOF){ insert(n),++n; } memset(f, -1, sizeof(f)); int ans = 0; for (int i = 0; i < n; i++){ int t = dp(i); if (ans < t) ans = t; } printf("%d\n", ans+1); return 0; }