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Problem1.py

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+class Solution(object):
+    def productExceptSelf(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: List[int]
+        """
+        # Time complexity: O(n)
+        # Space complexity: O(1) (excluding the output array)
+        #idea is to calculate the product from left to right
+        #and then from right to left
+        #eg: [1,2,3,4] : rightprod = [1,1,2,6], leftprod = [24,12,4,1] 
+        n = len(nums)
+        result = [1]* n
+        result[0] = 1
+        rightprod = 1
+        for i in range(n):
+            result[i] = rightprod
+            rightprod *= nums[i]
+
+
+        # Pass 2: right product
+        rightprod = 1
+        for i in range(n - 1, -1, -1):
+            result[i] *= rightprod
+            rightprod *= nums[i]
+
+        return result

Problem2.py

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+class Solution(object):
+    def findDiagonalOrder(self, mat):
+        """
+        Time complexity O(m*n) Space complexity O(1)
+        :type mat: List[List[int]]
+        :rtype: List[int]
+        """
+        m = len(mat)
+        n = len(mat[0])
+        result = [0 for _ in range(m*n)]
+        i,j = 0,0
+        dir = True
+        for idx in range(0, m*n):
+            result[idx] = mat[i][j]
+            if(dir):
+                if(i==0 and j!=n-1):
+                    dir = False
+                    j+=1
+                elif(j==n-1):
+                    dir = False
+                    i+=1
+                else:
+                    i-=1
+                    j+=1
+            else:
+                if(j==0 and i!=m-1):
+                    dir = True
+                    i+=1
+                elif(i==m-1):
+                    dir = True
+                    j+=1
+                else:
+                    j-=1
+                    i+=1
+        return result
+

Problem3.py

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+class Solution(object):
+    def spiralOrder(self, matrix):
+        """
+        Time complexity O(m*n) Space complexity O(1)
+        :type matrix: List[List[int]]
+        :rtype: List[int]
+        """
+        res = []
+        m = len(matrix)
+        n = len(matrix[0])
+        top = 0
+        bottom = m-1
+        left = 0
+        right = n-1
+        if not matrix or not matrix[0]:
+            return res
+
+        while(top<=bottom and left<=right):
+            for j in range(left, right+1):
+                res.append(matrix[top][j])
+            top+=1
+
+            for i in range(top, bottom+1):
+                res.append(matrix[i][right])
+            right-=1
+            if(top<=bottom):
+                for j in range(right, left-1,-1):
+                    res.append(matrix[bottom][j])
+                bottom-=1
+            if(left<=right):
+                for i in range(bottom, top-1,-1):
+                    res.append(matrix[i][left])
+                left+=1
+        return res
+