From 1340e539cfb2a6964a420657403e1ab6bc791b53 Mon Sep 17 00:00:00 2001
From: mihirs16 <mihirs16@gmail.com>
Date: Sat, 25 Feb 2023 12:19:19 +0000
Subject: [PATCH 1/2] added: target sum

---
 14. Questions/leetcode 494 - target sum.py | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)
 create mode 100644 14. Questions/leetcode 494 - target sum.py

diff --git a/14. Questions/leetcode 494 - target sum.py b/14. Questions/leetcode 494 - target sum.py
new file mode 100644
index 0000000..ddc9e1b
--- /dev/null
+++ b/14. Questions/leetcode 494 - target sum.py	
@@ -0,0 +1,22 @@
+# target sum | leetcode 494 | https://leetcode.com/problems/target-sum/
+# 0/1 knapsack to decide +/- and cache (index, total)
+
+class Solution:
+    def findTargetSumWays(self, nums: list[int], target: int) -> int:
+        N = len(nums)
+        mem = dict()
+
+        if N == 0:
+            return 0
+
+        def knapsack(n, s):
+            if n == N:
+                return 1 if s == target else 0
+            
+            if (n, s) in mem:
+                return mem[(n, s)]
+            
+            mem[(n, s)] = knapsack(n+1, s + nums[n]) + knapsack(n+1, s - nums[n])
+            return mem[(n, s)]
+
+        return knapsack(0, 0)

From 40c285cff56cc56aee3ba7d176b045e74b622a89 Mon Sep 17 00:00:00 2001
From: mihirs16 <mihirs16@gmail.com>
Date: Tue, 28 Feb 2023 01:18:42 +0000
Subject: [PATCH 2/2] added: construct quad trees

---
 .../leetcode 427 - construct quad tree.py     | 37 +++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 14. Questions/leetcode 427 - construct quad tree.py

diff --git a/14. Questions/leetcode 427 - construct quad tree.py b/14. Questions/leetcode 427 - construct quad tree.py
new file mode 100644
index 0000000..f2dba66
--- /dev/null
+++ b/14. Questions/leetcode 427 - construct quad tree.py	
@@ -0,0 +1,37 @@
+# construct quad tree | leetcode 427 | https://leetcode.com/problems/construct-quad-tree/
+# recursively call each quad of the grid and check if each quad is uniform or not
+
+# Definition for a QuadTree node.
+class Node:
+    def __init__(self, val, isLeaf, topLeft, topRight, bottomLeft, bottomRight):
+        self.val = val
+        self.isLeaf = isLeaf
+        self.topLeft = topLeft
+        self.topRight = topRight
+        self.bottomLeft = bottomLeft
+        self.bottomRight = bottomRight
+
+
+class Solution:
+    def construct(self, grid: list[list[int]]) -> Node:
+        def checkThisQuad(row, col, n) -> bool:
+            for i in range(row, row + n):
+                for j in range(col, col + n):
+                    if grid[i][j] != grid[row][col]:
+                        return False
+            return True
+
+        def quadTree(row, col, n):
+            if checkThisQuad(row, col, n):
+                return Node(grid[row][col], 1, None, None, None, None)
+            
+
+            return Node(grid[row][col], 0,
+                quadTree(row, col, n//2), 
+                quadTree(row, col + n//2, n//2),
+                quadTree(row + n//2, col, n//2),
+                quadTree(row + n//2, col + n//2, n//2)
+            )
+
+        return quadTree(0, 0, len(grid))
+