From a3f03ffe7dcf2697b1e5f2778f70e5d9774ac223 Mon Sep 17 00:00:00 2001
From: Srijha-Kalyan <87617310+Srijha-Kalyan@users.noreply.github.com>
Date: Mon, 17 Nov 2025 19:27:37 -0500
Subject: [PATCH 1/2] Add files via upload

---
 Problem1_1D_array_approach.py             | 29 +++++++++++++++++
 Problem1_exhaustive_approach.py           | 33 +++++++++++++++++++
 Problem1_memo_approach.py                 | 37 +++++++++++++++++++++
 Problem1_tabular_approach.py              | 29 +++++++++++++++++
 Problem2_paint_house_naive.py             | 39 +++++++++++++++++++++++
 Problem2_paint_house_space_optimal_Sol.py | 23 +++++++++++++
 Problem2_paint_house_tabular_bottom_up.py | 18 +++++++++++
 Problem2_paint_house_tabular_top_down.py  | 18 +++++++++++
 8 files changed, 226 insertions(+)
 create mode 100644 Problem1_1D_array_approach.py
 create mode 100644 Problem1_exhaustive_approach.py
 create mode 100644 Problem1_memo_approach.py
 create mode 100644 Problem1_tabular_approach.py
 create mode 100644 Problem2_paint_house_naive.py
 create mode 100644 Problem2_paint_house_space_optimal_Sol.py
 create mode 100644 Problem2_paint_house_tabular_bottom_up.py
 create mode 100644 Problem2_paint_house_tabular_top_down.py

diff --git a/Problem1_1D_array_approach.py b/Problem1_1D_array_approach.py
new file mode 100644
index 00000000..e96e67f3
--- /dev/null
+++ b/Problem1_1D_array_approach.py
@@ -0,0 +1,29 @@
+class Solution(object):
+    def coinChange(self, coins, amount):
+        """
+        There are two choices here: either not choosing a coin or choosing a coin and adding 1 to it
+        Time complexity O(m*n), space complexity: O(n) where m is length of coin array and n is amount
+        :type coins: List[int]
+        :type amount: int
+        :rtype: int
+        """
+        m = len(coins)
+        n = amount
+
+        dp = [99999 * (n+1)]
+        dp[0] = 0
+
+        for j in range(1, m+1):
+            dp[j] = -1
+        
+        for coin in coins:
+            for j in range(1, m+1):
+                if j < coin:
+                    dp[j] = dp[j]
+                else:
+                    dp[j] = dp[j] + dp[j - coin]+1
+        
+        if dp[n]==99999:
+            return -1
+        else:
+            return dp[n]
\ No newline at end of file
diff --git a/Problem1_exhaustive_approach.py b/Problem1_exhaustive_approach.py
new file mode 100644
index 00000000..5a1c5500
--- /dev/null
+++ b/Problem1_exhaustive_approach.py
@@ -0,0 +1,33 @@
+import sys
+class Solution(object):
+    def coinChange(self, coins, amount):
+        """
+        The exhaustive approach takes the addition of all possible combinations
+        Time complexity: 2^(n*m) n is length of coin array and m is amount
+        :type coins: List[int]
+        :type amount: int
+        :rtype: int
+        """
+        re = self.helper(coins, amount, 0)
+        #coins = [2], amount = 3 you can make any amount give here, 
+        # if ive gone out of bounds  
+        if re >= sys.maxsize:
+            return -1
+        return re
+    
+    def helper(self, coins, amount, idx):
+        #base case
+        if (amount==0):
+            return 0
+        #the amount becomes negative — this path is invalid
+        if amount < 0 or idx == len(coins):
+            return sys.maxsize
+
+        #logic
+        #case 1 - dont choose
+        case1 = self.helper(coins, amount, idx+1)
+        #case2 - choose
+        #add +1 because I just chose that one coin in the current index
+        case2 = 1 + self.helper(coins, amount-coins[idx], idx)
+
+        return case1 + case2
\ No newline at end of file
diff --git a/Problem1_memo_approach.py b/Problem1_memo_approach.py
new file mode 100644
index 00000000..07c5637c
--- /dev/null
+++ b/Problem1_memo_approach.py
@@ -0,0 +1,37 @@
+class Solution(object):
+    def coinChange(self, coins, amount):
+        """
+        Time complexity O(m*n), Space: O(m*n) where m is length of coin array and n is amount
+        :type coins: List[int]
+        :type amount: int
+        :rtype: int
+        """
+        re = self.helper(coins, amount, 0)
+        #coins = [2], amount = 3 you can make any amount give here, 
+        # if ive gone out of bounds  
+        m = len(coins)
+        n = amount
+        self.memo = [[0] * (n + 1) for _ in range(m + 1)]
+        if re >= 99999:
+            return -1
+        return re
+    
+    def helper(self, coins, amount, idx):
+        #base case
+        if (amount==0):
+            return 0
+        #the amount becomes negative — this path is invalid
+        if amount < 0 or idx == len(coins):
+            return 99999
+
+        if self.memo[idx][amount] != 0:
+            return  self.memo[idx][amount]
+        #logic
+        #case 1 - dont choose
+        case1 = self.helper(coins, amount, idx+1)
+        #case2 - choose
+        #add +1 because I just chose that one coin in the current index
+        case2 = 1 + self.helper(coins, amount-coins[idx], idx)
+
+        self.memo[idx][amount] = case1 + case2
+        return self.memo[idx][amount]
\ No newline at end of file
diff --git a/Problem1_tabular_approach.py b/Problem1_tabular_approach.py
new file mode 100644
index 00000000..7024fe68
--- /dev/null
+++ b/Problem1_tabular_approach.py
@@ -0,0 +1,29 @@
+class Solution(object):
+    def coinChange(self, coins, amount):
+        """
+        There are two choices here: either not choosing a coin or choosing a coin and adding 1 to it
+        Time complexity O(m*n), space complexity: O(m*n) where m is length of coin array and n is amount
+        :type coins: List[int]
+        :type amount: int
+        :rtype: int
+        """
+        m = len(coins)
+        n = amount
+
+        dp = [[0] * (n+1) for _ in range(m+1)]
+
+
+        for j in range(1, m+1):
+            dp[0][j] = -1
+        
+        for i in range(1, n+1):
+            for j in range(1, m+1):
+                if j < coins[i-1]:
+                    dp[i][j] = dp[i-1][j]
+                else:
+                    dp[i][j] = dp[i-1][j] + dp[i][j - coins[i-1]]+1
+        
+        if dp[m][n]==99999:
+            return -1
+        else:
+            return dp[m][n]
\ No newline at end of file
diff --git a/Problem2_paint_house_naive.py b/Problem2_paint_house_naive.py
new file mode 100644
index 00000000..da50a9eb
--- /dev/null
+++ b/Problem2_paint_house_naive.py
@@ -0,0 +1,39 @@
+class Solution:
+    #exhaustive approach of trying out all possibilities and the time complexity 
+    # is m*2^n where m is number of colors
+    def minCost(self, costs):  # 0-R, 1-B, 2-G
+        colorR = self.helper(costs, 0, 0, 0)
+        colorB = self.helper(costs, 0, 1, 0)
+        colorG = self.helper(costs, 0, 2, 0)
+        #return the minimum cost out of all the 3 colors
+        return min(colorR, colorB, colorG)
+
+    def helper(self, costs, i, color, totalCost):
+        #base
+        # If we’ve already painted all houses (index i has reached the end of the list),
+        # then there are no more recursive choices to make,
+        # so we just return the accumulated total cost.
+        if(i==len(costs)):
+            return totalCost
+
+        #logic 
+        #if color is Red
+        if(color == 0):
+            #2 possibilities
+            colorB = self.helper(costs, i+1, 1)
+            colorG = self.helper(costs, i+1, 2)
+            return costs[i][0] + min(colorB, colorG)
+        
+        #color is blue
+        elif(color == 1):
+            colorR = self.helper(costs, i+1, 0)
+            colorG = self.helper(costs, i+1, 2)
+            return costs[i][1] + min(colorR, colorG)
+        
+        #Green
+        elif(color == 2):
+            colorR = self.helper(costs, i+1, 0)
+            colorB = self.helper(costs, i+1, 1)
+            return costs[i][1] + min(colorR, colorB)
+        
+        return max.size()
\ No newline at end of file
diff --git a/Problem2_paint_house_space_optimal_Sol.py b/Problem2_paint_house_space_optimal_Sol.py
new file mode 100644
index 00000000..7b6c9a7a
--- /dev/null
+++ b/Problem2_paint_house_space_optimal_Sol.py
@@ -0,0 +1,23 @@
+class Solution:
+    #Time complexity O(n) Space is O(1) since variable stored in temp var
+    def minCost(self, costs):  # 0-R, 1-B, 2-G
+        n = len(costs) #rows of houses
+        m = len(costs[0]) #cols of diff colors
+        dp = [[0] * n for _ in range(m)]
+
+        colorR = costs[n-1][0] #starting bottom up last red house
+        colorB = costs[n-1][1] #last blue house
+        colorG = costs[n-1][2] #last green house
+        min(colorR, colorB, colorG)
+
+        for i in range (n-2, -1, 1):
+            #WHENEVER YOU ARE MUTATING AN ORIGINAL VALUE STORE IT IN A TEMP ARRAY
+            #SO THAT ORGINAL VALUE CAN BE USED LATER
+            tempR = colorR
+            tempB = colorB
+            
+            colorR = costs[i][0] + min(colorB, colorG) #
+            colorB = costs[i][1] + min(tempR, colorG) #ORIGINAL DP[0] AKA COLORR
+            colorG = costs[i][2] + min(tempR, tempB) #ORIGINAL DP[1] AKA COLORB
+        re = min(dp[0][0], dp[0][1], dp[0][2])
+        return re
\ No newline at end of file
diff --git a/Problem2_paint_house_tabular_bottom_up.py b/Problem2_paint_house_tabular_bottom_up.py
new file mode 100644
index 00000000..6a402d7c
--- /dev/null
+++ b/Problem2_paint_house_tabular_bottom_up.py
@@ -0,0 +1,18 @@
+class Solution:
+    #Time complexity O(n)
+    def minCost(self, costs):  # 0-R, 1-B, 2-G
+        n = len(costs) #rows of houses
+        m = len(costs[0]) #cols of diff colors
+        dp = [[0] * n for _ in range(m)]
+
+        dp[n-1][0] = costs[n-1][0] #starting bottom up last red house
+        dp[n-1][1] = costs[n-1][1] #last blue house
+        dp[n-1][2] = costs[n-1][2] #last green house
+
+        for i in range (n-2, -1, 1):
+            dp[i][0] = costs[i][0] + min(dp[i+1][1], dp[i+1][2]) #
+            dp[i][1] = costs[i][1] + min(dp[i+1][0], dp[i+1][2])
+            dp[i][2] = costs[i][2] + min(dp[i+1][0], dp[i+1][1])
+        re = min(dp[0][0], dp[0][1], dp[0][2])
+        return re
+
diff --git a/Problem2_paint_house_tabular_top_down.py b/Problem2_paint_house_tabular_top_down.py
new file mode 100644
index 00000000..1f922251
--- /dev/null
+++ b/Problem2_paint_house_tabular_top_down.py
@@ -0,0 +1,18 @@
+class Solution:
+    #Time complexity O(n)
+    def minCost(self, costs):  # 0-R, 1-B, 2-G
+        n = len(costs) #rows of houses
+        m = len(costs[0]) #cols of diff colors
+        dp = [[0] * n for _ in range(m)]
+
+        dp[0][0] = costs[0][0] #starting bottom up last red house
+        dp[1][1] = costs[1][1] #last blue house
+        dp[2][2] = costs[2][2] #last green house
+
+        for i in range (1, n):
+            dp[i][0] = costs[i][0] + min(dp[i-1][1], dp[i-1][2]) #
+            dp[i][1] = costs[i][1] + min(dp[i-1][0], dp[i-1][2])
+            dp[i][2] = costs[i][2] + min(dp[i-1][0], dp[i-1][1])
+        re = min(dp[n-1][0], dp[n-1][1], dp[n-1][2])
+        return re
+

From 31c73cdc813d177e33755e892d051bd9f51e7796 Mon Sep 17 00:00:00 2001
From: Srijha-Kalyan <87617310+Srijha-Kalyan@users.noreply.github.com>
Date: Mon, 17 Nov 2025 19:43:09 -0500
Subject: [PATCH 2/2] Add files via upload

---
 Problem1_BFS.py             | 44 ++++++++++++++++++++++++++++++
 Problem1_BFS_Deque.py       | 53 +++++++++++++++++++++++++++++++++++++
 Problem2_Course_Schedule.py | 36 +++++++++++++++++++++++++
 3 files changed, 133 insertions(+)
 create mode 100644 Problem1_BFS.py
 create mode 100644 Problem1_BFS_Deque.py
 create mode 100644 Problem2_Course_Schedule.py

diff --git a/Problem1_BFS.py b/Problem1_BFS.py
new file mode 100644
index 00000000..e1754913
--- /dev/null
+++ b/Problem1_BFS.py
@@ -0,0 +1,44 @@
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution(object):
+    def levelOrder(self, root):
+        """
+        :type root: Optional[TreeNode]
+        :rtype: List[List[int]]
+
+            1
+         2     3
+        4 5   6 7         
+        o/p: 
+        [
+        [1],
+        [2,3],
+        [4,5,6,7]
+        ]
+        We need to keep track of level list and rsult adds the lists
+        queue takes root and next_queue adds left and right children
+        Time complexity:O(N)
+        Space Complexity: O(h) where h is height of tree
+        """
+        if root is None:
+            return []
+        queue = [root]
+        level = []
+        result = []
+
+        while queue!=[]:
+            for root in queue:
+                level.append(root.val)
+                if root.left is not None:
+                    next_queue.append(root.left)
+                if root.right is not None:
+                    next_queue.append(root.right)
+            result.append(level)
+            level = []
+            queue = next_queue
+            next_queue = []
+        return result
diff --git a/Problem1_BFS_Deque.py b/Problem1_BFS_Deque.py
new file mode 100644
index 00000000..290b58a7
--- /dev/null
+++ b/Problem1_BFS_Deque.py
@@ -0,0 +1,53 @@
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = rig
+from collections import deque 
+class Solution(object):
+    def levelOrder(self, root):
+        """
+        :type root: Optional[TreeNode]
+        :rtype: List[List[int]]
+
+            1
+         2     3
+        4 5   6 7         
+        o/p: 
+        [
+        [1],
+        [2,3],
+        [4,5,6,7]
+        ]
+        We need to keep track of level list and rsult adds the lists
+        queue takes root and next_queue adds left and right children
+        Time complexity:O(N)
+        Space Complexity: O(h) where h is height of tree
+        """
+        if root is None:
+            return []
+        queue = deque([root])
+        level = 0
+        level_list = []
+        result = []
+
+        while queue:
+            for _ in range(len(queue)):
+                curr_root = queue.popleft()
+                level_list.append(curr_root.val)
+                print(level_list)
+                if curr_root.left is not None:
+                    queue.append(curr_root.left)
+                if curr_root.right is not None:
+                    queue.append(curr_root.right)
+            result.append(level_list)
+            level+=1
+            level_list = []
+        return result
diff --git a/Problem2_Course_Schedule.py b/Problem2_Course_Schedule.py
new file mode 100644
index 00000000..6608affe
--- /dev/null
+++ b/Problem2_Course_Schedule.py
@@ -0,0 +1,36 @@
+from collections import defaultdict
+class Solution(object):
+    def canFinish(self, numCourses, prerequisites):
+        """
+        The idea is to return false when a cycle is detected
+        add the couese number in key and list as values
+        Time complexity: O(P+C) where C is number of courses and P is number of edges(prerequisites)
+        Space Complexity: O(P+C) for the hashtable
+        :type numCourses: int
+        :type prerequisites: List[List[int]]
+        :rtype: bool
+        """
+        prereqs =  defaultdict(list)
+        #add the courses and prereqs in this hastable
+        for c, p in prerequisites:
+            prereqs[c].append(p)
+        
+        seen = set()
+        
+        def cycle(course, seen):
+            if course in seen:
+                return True
+
+            seen.add(course)
+            for p in prereqs[course]:
+                if cycle(p, seen):
+                    return True
+            prereqs[course] = []
+            seen.remove(course)
+            return False
+        
+        
+        for course in range(numCourses):
+            if cycle(course, seen):
+                return False
+        return True
\ No newline at end of file