added 79 word search

Author: mahesh-3pillar

README.md

@@ -5,8 +5,21 @@ https://sebinsua.com/algorithmic-bathwater
 https://sebinsua.com/assets/posts/algorithmic-bathwater/algorithmic-bathwater-1.svg
 
 
+# 79. Word Search
+Intuition: Explore all possible path to find a matching work hence backtracking
+
+Approach:
+1. dfs i, j, word
+   1. if word len is 0 return True
+   2. if i or j out of boundary or word[0] is neq board[i][j] return false
+   3. store board[i][j] in tmp and set board[i][j] to `#` // so that it can be avoided to revisit
+   4. move all four direction for remaining word (word[1:]) and compute the result
+   5. reset board[i][j] to original word
+   6. return the computed result from all four direction move
+2. call dfs for each row and col of board
 
 
+----
 # 2405: Optimal Partition of String
 
 Intuition: map to store the string char, if char already exists in map means with hit a non unique char, increase the count and reset the map

leetcode-py/79-word-search.py

@@ -0,0 +1,32 @@
+class Solution:
+    def exist(self, board: List[List[str]], word: str) -> bool:
+        ROW = len(board)
+        COL = len(board[0])
+
+        def dfs(i, j, word):
+            #End of the word, hence true
+            if len(word) == 0:
+                return True
+            # out of the boundary or char is not exist at i & j
+            if i<0 or i>=ROW or j<0 or j>=COL or board[i][j] != word[0]:
+                return False
+            
+            # store in tmp and will be use in reset for next iteration
+            tmp = board[i][j] # chose
+
+            # mark visited for current visit
+            board[i][j] = "#"
+
+            #explore
+            res = dfs(i+1, j, word[1:]) or dfs(i-1, j, word[1:]) or dfs(i, j+1, word[1:]) or dfs(i, j-1, word[1:])
+    
+            #un-chose
+            board[i][j] = tmp
+            return res
+        
+        for i in range(ROW):
+            for j in range(COL):
+                if dfs(i, j, word): #choice 
+                    return True
+        
+        return False