[Leetcode] Word Search

最新推荐文章于 2019-05-21 18:57:38 发布

原创最新推荐文章于 2019-05-21 18:57:38 发布 · 481 阅读

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本文介绍了一种算法，用于在一个二维字符网格中查找指定的单词。该算法通过深度优先搜索逐个匹配单词中的字母，并确保不重复使用相同的字母格。文中提供了两种实现方式，包括递归方法和使用栈的数据结构。

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Given a 2D board and a word, find if the word exists in the grid.

The word can 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.

For example,
Given board =

[
  ["ABCE"],
  ["SFCS"],
  ["ADEE"]
]

word = "ABCCED", -> returns true,
word = "SEE", -> returns true,
word = "ABCB", -> returns false.

class Solution {
public:
    bool exist(vector<vector<char> > &board, string word) {
        int n = board.size();
        if (n == 0) return false;
        int m = board[0].size();
        set<pair<int,int> >s;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (check(board, word, i, j, 0, s) == true) return true;
            }
        }
        return false;
    }
    
    bool check(vector<vector<char> >&a, string& w, int x, int y, int cnt, set<pair<int,int> >&s) {
        if (cnt == w.size()) return true;
		if (x >= a.size() || x < 0 || y >= a[0].size() || y < 0) return false;
        if (s.count(make_pair(x,y)) > 0)return false;
        if (w[cnt] != a[x][y]) return false;
        s.insert(make_pair(x,y));
        int dx[] = {0,0,1,-1};
        int dy[] = {1,-1,0,0};
        for (int i = 0; i < 4; i++) {
            if (check(a, w, x+dx[i], y+dy[i], cnt+1, s) == true) return true;
        }
        s.erase(make_pair(x,y));
        return false;
    } 
};

class coordinate{
    public:
    int x;
    int y;
};
class Solution {
public:
bool isAvailable(vector<vector<char> > &board,int row,int column,char c){
        if(row<0||row>=board.size()){
            return false;
        }
        vector<char> &tmpV=board[row];
        if(column<0||column>=tmpV.size()){
            return false;
        }
        if(tmpV[column]==c){
            tmpV[column]=0;
           
            return true;
        }
    }
    bool exist(vector<vector<char> > &board, string word) {
        int wordindex=0;
        if(word.size()<=0){
            return true;
        }
        stack<int> ds;
        stack<coordinate> Coo;
        for(int i=0;i<board.size();i++){
            vector<char> &tmpV=board[i];
            for(int j=0;j<tmpV.size();j++){
                    if(word[0]!=tmpV[j]){
                        continue;
                    }
                 //   cout<<"i:"<<i<<"j:"<<j<<endl;
                    tmpV[j]=0;
                    int oldi=i,oldj=j;
                    wordindex=1;
                    ds.push(0);
                     coordinate coo;
                     coo.x=oldi;
                     coo.y=oldj;
                     Coo.push(coo);
                    int oldd=0;
                    while(wordindex>=1){
                        if(wordindex>word.size()-1){
                            return true;    
                        }
                        char c=word[wordindex];
                   //     cout<<"oldi :"<<oldi<<"oldj: "<<oldj<<"  c:"<<c<<endl;
                        if(oldd<1){
                            if(isAvailable(board,oldi-1,oldj,c)){
                                 wordindex++;
                                 ds.push(1);
                                 coordinate coo;
                                coo.x=oldi-1;
                                  coo.y=oldj;
                                 Coo.push(coo);
                                 oldd=0;
                                 oldi=oldi-1;
                                 oldj=oldj;
                                 continue;
                            }
                        }
                 //       cout<<"1"<<endl;
                        if(oldd<2){
                            if(isAvailable(board,oldi+1,oldj,c)){
                                 wordindex++;
                                 ds.push(2);
                                 coordinate coo;
                                coo.x=oldi+1;
                                  coo.y=oldj;
                                 Coo.push(coo);
                                 oldd=0;
                                 oldi=oldi+1;
                                 oldj=oldj;
                                 continue;
                            }
                        }
                //         cout<<"2"<<endl;
                        if(oldd<3){
                            if(isAvailable(board,oldi,oldj-1,c)){
                                 wordindex++;
                                 ds.push(3);
                                 coordinate coo;
                                coo.x=oldi;
                                  coo.y=oldj-1;
                                 Coo.push(coo);
                                 oldd=0;
                                 oldi=oldi;
                                 oldj=oldj-1;
                                 continue;
                            }
                        }
                      //   cout<<"3"<<endl;
                        if(oldd<4){
                            if(isAvailable(board,oldi,oldj+1,c)){
                                 wordindex++;
                                 ds.push(4);
                                 coordinate coo;
                                coo.x=oldi;
                                  coo.y=oldj+1;
                                 Coo.push(coo);
                                 oldd=0;
                                 oldi=oldi;
                                 oldj=oldj+1;
                                 continue;
                            }
                        }
                     //    cout<<"4"<<endl;
                        wordindex--;
                        coordinate coo;
                        coo=Coo.top();
                        Coo.pop();
                        board[coo.x][coo.y]=word[wordindex];
                      if(wordindex>0){
                      coo=Coo.top();
                        oldi=coo.x;
                        oldj=coo.y;
                        oldd=ds.top();
                        ds.pop();
                      }
                    }
                }
        }
            
        
        return false;
    }
};

用时：136s