Create week 5 79. Word Search

Author: andysli6590

week 5 79. Word Search

@@ -0,0 +1,33 @@
+public class Solution {
+    public boolean exist(char[][] board, String word) {
+        if(word == null || word.length() == 0){
+            return true;
+        }
+        char[] str = word.toCharArray();
+        
+        for (int i = 0; i < board.length; i++){
+            for(int j = 0; j < board[0].length; j++){
+                if (helper(board, str, i, j, 0)){
+                    return true;
+                }
+            }
+        }
+        return false;
+    }
+    public boolean helper (char [][] board, char[] str, int i, int j, int pos){
+        if(pos == str.length){
+            return true;
+        }
+if (i < 0 || i >= board.length || j < 0 || j >= board[0].length || board[i][j] != str[pos]){
+            return false;
+        }
+        char cur = board [i] [j];
+        board [i] [j] = '$';
+        boolean res = helper (board, str, i - 1, j, pos + 1)
+                    ||helper (board, str, i + 1, j, pos + 1)
+                    ||helper (board, str, i, j - 1, pos + 1) 
+                    ||helper (board, str, i, j + 1, pos + 1);
+    board [i] [j] = cur;
+    return res;
+    }
+}