a1

diagonal-traverse.py

@@ -0,0 +1,42 @@
+
+# O(m*n) time, O(m*n) space
+
+# start with a flat array of length of m*n, iterate through that array, moving right and left pointers depending on boundaries
+# top left, bottom right, column is 0, row is 0. Flag is True means going up, Flag false means going down
+
+class Solution:
+	def findDiagonalOrder(self, mat: List[List[int]]) -> List[int]:
+		m = len(mat)
+		n = len(mat[0])
+
+		res = [0]*(n*m)
+
+		flag = True # True going up, False going down
+
+		r=0
+		c=0
+		for i in range(len(res)):
+			res[i] = mat[r][c]
+			if flag:
+				if c == n-1:
+					r+=1
+					flag = False 
+				elif r == 0:
+					c+=1
+					flag = False 
+				else:
+					r-=1
+					c+=1
+			else:
+				if r == m-1:
+					c+=1
+					flag=True
+				elif c == 0:
+					r+=1
+					flag=True 
+				else:
+					r+=1
+					c-=1
+
+		return res
+

product-array-self.py

@@ -0,0 +1,21 @@
+
+# time O(n), space O(n)
+
+# iterate through res to first generate prefixes, then take prefixes and multiply by suffix in opposite order
+class Solution:
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+
+        # nums = [1,2,3,4]
+        res = [1]*len(nums)
+
+        prefix = 1
+        for i in range(len(nums)):
+            res[i]*=prefix 
+            prefix*=nums[i]
+
+        suffix = 1
+        for i in range(len(nums)-1,-1,-1):
+            res[i]*=suffix 
+            suffix*=nums[i] 
+
+        return res

spiral-matrix.py

@@ -0,0 +1,36 @@
+
+# time O(n*m), space O(n*m)
+# track top, left, right, bottom pointers and iterate through the spiral of the matrix, adding each matrix value to result
+class Solution:
+    def spiralOrder(self, matrix: List[List[int]]) -> List[int]:
+        result = []
+
+        n = len(matrix) # rows
+        m = len(matrix[0]) # cols
+
+        left = 0
+        right = m - 1
+        top = 0
+        bottom = n - 1
+
+        while left <= right and top <= bottom: 
+            for c in range(left, right+1):
+                result.append(matrix[top][c])
+            top+=1
+            for r in range(top,bottom+1):
+                result.append(matrix[r][right])
+            right-=1
+
+            if not (left <= right and top <= bottom):
+                break 
+
+            for c in range(right, left-1,-1):
+                result.append(matrix[bottom][c])
+            bottom -= 1
+            for r in range(bottom, top-1, -1):
+                result.append(matrix[r][left])
+            left+=1
+
+
+
+        return result