-
Notifications
You must be signed in to change notification settings - Fork 0
/
WordSearchII.cpp
56 lines (52 loc) · 1.77 KB
/
WordSearchII.cpp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
#include <vector>
#include <string>
using namespace std;
struct TrieNode{
int idx;
TrieNode *next[26];
TrieNode():idx(-1){memset(next,0,sizeof(next));};
};
class Solution {
public:
/* Sol 0
* Use a Trie to find words efficiently.
* Firstly, build the Trie using words, then for each char in board, search the word in the trie.
* Note when backtracking, recover the char from '#' to its original value.
*/
vector<string> findWords(vector<vector<char> >& board, vector<string>& words) {
vector<string> result;
TrieNode *root = new TrieNode();
buildTrie(root,words);
for(int i = 0;i < board.size();++i){
for(int j = 0;j < board[0].size();++j){
dfs(result,board,i,j,root,words);
}
}
return result;
}
void dfs(vector<string> &result, vector<vector<char> > &board,int i,int j,TrieNode *p,vector<string> &words){
char c = board[i][j];
if(c == '#' || p->next[c - 'a'] == nullptr) return;
p = p->next[c-'a'];
if(p->idx != -1) {
result.push_back(words[p->idx]);
p->idx = -1; // avoid duplicated word
}
board[i][j] = '#';
if(i > 0) dfs(result,board,i-1,j,p,words);
if(j > 0) dfs(result,board,i,j-1,p,words);
if(i+1 < board.size()) dfs(result,board,i+1,j,p,words);
if(j+1 < board[0].size()) dfs(result,board,i,j+1,p,words);
board[i][j] = c;
}
void buildTrie(TrieNode *root,vector<string>& words){
for(int i = 0;i < words.size();++i){
TrieNode *p = root;
for(auto c:words[i]){
if(p->next[c-'a']==nullptr) p->next[c-'a'] = new TrieNode();
p = p->next[c-'a'];
}
p->idx = i;
}
}
};