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最新推荐文章于 2025-02-17 17:10:41 发布

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本文介绍了一个解决WordSearch II问题的算法实现。该问题要求在一个二维字符矩阵中找出所有由相邻字母组成的字典中的单词。文章详细阐述了算法的思路与实现细节，并通过具体的代码展示了如何进行高效搜索。

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Word Search II

Given a 2D board and a list of words from the dictionary, find all words in the board.

Each word must be constructed from letters of sequentially adjacent cell, where “adjacent” cells are those horizontally or vertically neighboring. The same letter cell may not be used more than once in a word.

For example,
Given words = [“oath”,”pea”,”eat”,”rain”] and board =

[
[‘o’,’a’,’a’,’n’],
[‘e’,’t’,’a’,’e’],
[‘i’,’h’,’k’,’r’],
[‘i’,’f’,’l’,’v’]
]
Return [“eat”,”oath”].
Note:
You may assume that all inputs are consist of lowercase letters a-z.

typedef pair<int, int> pint;
auto isLeftOK = [](const size_t &L, const size_t &R, char c, vector<vector<char>>& board, vector<vector<bool>> &vvb)->bool{
        if (R < 1) return false;
        else if ( !vvb[L][R-1] && c == board[L][R-1]) return true;
        else return false;
    };
    auto isRightOK = [](const size_t &L, const size_t &R, char c, vector<vector<char>>& board, vector<vector<bool>> &vvb)->bool{
        if (R+1 >= board[0].size()) return false;
        else if ( !vvb[L][R+1] && c == board[L][R+1]) return true;
        else return false;
    };
    auto isUpOK = [](const size_t &L, const size_t &R, char c, vector<vector<char>>& board, vector<vector<bool>> &vvb)->bool{
        if (L < 1) return false;
        else if ( !vvb[L-1][R] && c == board[L-1][R]) return true;
        else return false;
    };
    auto isDownOK = [](const size_t &L, const size_t &R, char c, vector<vector<char>>& board, vector<vector<bool>> &vvb)->bool{
        if (L+1 >= board.size()) return false;
        else if ( !vvb[L+1][R] && c == board[L+1][R]) return true;
        else return false;
    };
class Solution {
public:
    unordered_multimap<char, pair<int, int>> mmps;
    typedef pair<int,int> pint;
    bool isIn(vector<vector<char>>& board, string &word, size_t index, size_t L, size_t R, vector<vector<bool>> &vvb) {
        if (index >= word.size()) return true;
        if (isLeftOK(L, R, word[index], board, vvb)) {
            vvb[L][R-1] = true;
            if( isIn(board, word, index+1, L, R-1, vvb)) 
            {
                vvb[L][R-1] = false;
                return true;
            }
            vvb[L][R-1] = false;
        }
        if (isRightOK(L, R, word[index], board, vvb)) {
            vvb[L][R+1] = true;
            if (isIn(board, word, index+1, L, R+1, vvb)) {
                vvb[L][R+1] = false;
                return true;
            }
            vvb[L][R+1] = false;
        }
        if (isUpOK(L, R, word[index], board, vvb)) {
            vvb[L-1][R] = true;
            if (isIn(board, word, index+1, L-1, R, vvb)) {
                vvb[L-1][R] = false;
                return true;
            }
            vvb[L-1][R] = false;
        }
        if (isDownOK(L, R, word[index], board, vvb)) {
            vvb[L+1][R] = true;
            if (isIn(board, word, index+1, L+1, R, vvb)) {
                vvb[L+1][R] = false;
                return true;
            }
            vvb[L+1][R] = false;
        }
        return false;
    }
    //
    bool isInBoard(vector<vector<char>>& board, string &word) {
    string word0(word.rbegin(), word.rend());
    bool res;
    if (mmps.empty()) {

            for (size_t i = 0; i < board.size(); ++i) {

                for (size_t j = 0; j < board[i].size(); ++j) {
                    mmps.insert(pair<char, pint>(board[i][j], pint(i,j)));
                }

        }
    }
     vector<vector<bool>> vvb(board.size(), vector<bool>(board[0].size(), false));
    // forward
    char c = word[0];
    auto resfs = mmps.equal_range(c);
    for (auto it = resfs.first; it != resfs.second; it++) {
        res = false;
        vvb[it->second.first][it->second.second] = true;
        res = isIn(board, word, 1, it->second.first, it->second.second, vvb);
        vvb[it->second.first][it->second.second] = false;
        if (res) return res;
    }
    // reverse
    c = word0[0];
    resfs = mmps.equal_range(c);
    for (auto it = resfs.first; it != resfs.second; it++) {
        res = false;
        vvb[it->second.first][it->second.second] = true;
        res = isIn(board, word0, 1, it->second.first, it->second.second, vvb);
        vvb[it->second.first][it->second.second] = false;
        if (res) return res;
    }
    return false;

}
    vector<string> findWords(vector<vector<char>>& board, vector<string>& words) {
        vector<string> res;
        unordered_set<string> s1(words.begin(), words.end());
        vector<string> words0(s1.begin(), s1.end());
        for (auto &i : words0) {
            if (isInBoard(board, i)) 
                res.push_back(i);
        }
        return res;
    }
};