Word Search

bool flag;
class Solution {
public:
bool exist(vector<vector<char> >& board, string word) {
flag = 0;
if(board.size()*board[0].size() < word.length())
return false;
bool tag[100][100];
int i,j;
for(i=0;i<100;i++){
for(j=0;j<100;j++)
tag[i][j] = 0;
}
bool retval = 0;
for(i=0;i<board.size();i++){
for(j=0;j<board[0].size();j++){
if(board[i][j] == word[0]){
tag[i][j] = 1;
retval = dfsSearch(board,word,i,j,1,tag);
tag[i][j] = 0;
}

if(retval)
return retval;
}
}
return retval;
}
bool dfsSearch(vector<vector<char> > &board,string word,int x,int y,int pos,bool a[100][100]){
if(flag)
return true;
if(pos == word.length()){
flag = 1;
return true;
}
if(!flag && x-1 >=0 && a[x-1][y]!=1 && board[x-1][y] == word[pos]){
a[x-1][y] = 1;
dfsSearch(board,word,x-1,y,pos+1,a);
a[x-1][y] = 0;
}
if(!flag && y+1 < board[0].size() && a[x][y+1]!=1 && board[x][y+1] == word[pos]){
a[x][y+1] = 1;
dfsSearch(board,word,x,y+1,pos+1,a);
a[x][y+1] = 0;
}
if(!flag && x+1 < board.size() && a[x+1][y]!=1 && board[x+1][y] == word[pos]){
a[x+1][y] = 1;
dfsSearch(board,word,x+1,y,pos+1,a);
a[x+1][y] = 0;
}
if(!flag && y-1 >= 0 && a[x][y-1]!=1 && board[x][y-1] == word[pos]){
a[x][y-1] = 1;
dfsSearch(board,word,x,y-1,pos+1,a);
a[x][y-1] = 0;
}
return flag;
}
};