added code

Author: ShashankSinha98

16. Recursion and backtracking/19. N Queen.py

@@ -23,10 +23,12 @@ def n_queen(board,i,n):
 
             thisQueenPosIsValid = n_queen(board,i+1,n)
 
+            board[i][j] = 0
+
             if thisQueenPosIsValid:
                 return True
 
-            board[i][j] = 0
+            #board[i][j] = 0
 
             unset_storage(board,i,j,n)
             #print_storage("C, j: "+str(j)+", i: "+str(i))

16. Recursion and backtracking/21. Sudoku Solver.py

@@ -20,10 +20,12 @@ def sudoku_solver(sudoku,i,j,n):
 
             can_sudoku_solve = sudoku_solver(sudoku,i,j+1,n)
 
+            sudoku[i][j] = 0
+
             if can_sudoku_solve:
                 return True
 
-    sudoku[i][j] = 0
+    #sudoku[i][j] = 0
 
     return False
 

44. Dynamic Programming/09. Ladders Top Down.py

@@ -11,8 +11,8 @@ def solve(n,k):
     ans = 0
     for i in range(1,k+1):
         if n-i>=0:
-            ans += dp[n-i] if dp[n-i] !=0 else solve(n-i,k)
+            ans += solve(n-i,k)
     dp[n] = ans
-    return dp[n]
+    return dp[n]    
 
 print(solve(4,3))

44. Dynamic Programming/13. Longest Common Subsequence.py

@@ -0,0 +1,68 @@
+a = "AGGTAB"
+b = "GXTXAYB"
+op = ""
+MAX = 3000
+dp = [[-1]*MAX for i in range(MAX)]
+
+def solve_topdown(a,b,i,j):
+
+    if j>=len(a) or i>=len(b):
+        return 0
+
+    if dp[i][j] != -1:
+        return dp[i][j]
+
+    ans = -1
+    if a[j] == b[i]:
+        ans = 1+solve_topdown(a,b,i+1,j+1)
+    else:
+        ans = max(solve_topdown(a,b,i+1,j),solve_topdown(a,b,i,j+1))
+    
+    dp[i][j] = ans
+
+    return ans
+
+
+
+
+def solve(a,b):
+    global op
+
+    la = len(a)
+    lb = len(b)
+
+    dp = [[0]*(la+1) for i in range(lb+1)]
+
+    for i in range(1,lb+1):
+        for j in range(1,la+1):
+            if a[j-1]==b[i-1]:
+                op += a[j-1]
+                dp[i][j] = dp[i-1][j-1] + 1
+            else:
+                dp[i][j] = max(dp[i-1][j],dp[i][j-1])
+    
+    return dp[lb][la],dp
+
+def get_LCS(a,b,l,dp):
+    
+    i = len(b)
+    j = len(a)
+    res = ""
+
+    while(l>0):
+        if a[j-1]==b[i-1]:
+            res = a[j-1] + res
+            i-=1
+            j-=1
+            l-=1
+        else:
+            if (dp[i][j-1]>dp[i-1][j]):
+                j-=1
+            else:
+                i-=1 
+    
+    return res
+
+l,dp = solve(a,b)
+#print(l,dp)
+print(get_LCS(a,b,l,dp))

46. DP Problems Set - II/1. Problem F - LCS.py

@@ -0,0 +1,46 @@
+MAX = 8
+dp = [[-1]*MAX for i in range(MAX)]
+
+def get_LCS_len(a,b,i,j):
+    global dp
+
+    if j>=len(a) or i>=len(b):
+        return 0
+
+    if dp[i][j] != -1:
+        return dp[i][j]
+
+    if a[j]==b[i]:
+        dp[i][j] = get_LCS_len(a,b,i+1,j+1) + 1
+    else:
+        dp[i][j] = max(get_LCS_len(a,b,i+1,j),get_LCS_len(a,b,i,j+1))
+
+    return dp[i][j]
+
+def get_LCS(a,b,l):
+    global dp
+    i = j = 0
+    res = ""
+
+    while(l>0):
+        if a[j]==b[i]:
+            res += a[j]
+            i+=1
+            j+=1
+            l-=1
+        else:
+            if (dp[i][j+1]>dp[i+1][j]):
+                j+=1
+            else:
+                i+=1 
+    
+    return res
+
+
+a = "AGGTAB"
+b = "GXTXAYB"
+
+l = get_LCS_len(a,b,0,0)
+print(get_LCS(a,b,l))
+print(dp)
+