Array-1 all problems added

Problem1.py

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+# https://leetcode.com/problems/product-of-array-except-self/
+# TC: O(3n) => O(n)
+# SC: O(n)
+
+# This solution uses running sum logic. Iterate through input array nums from left to right to calculate product of elements except that
+# element in res array. Second iteration will be iterating the nums array in reverse direction to calculate product of elements except 
+# that element, multiply the value of res[i] 
+
+class Solution:
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+        res = [1] * len(nums)
+
+        for i in range(1, len(nums)):
+            res[i] = res[i-1] * nums[i-1]
+
+        prod = 1
+        for i in range(len(nums) - 2, -1, -1):
+            prod = prod * nums[i+1]
+            res[i] = prod * res[i]
+
+        return res

Problem2.py

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+# https://leetcode.com/problems/diagonal-traverse/description/
+
+class Solution:
+    def findDiagonalOrder(self, mat: List[List[int]]) -> List[int]:
+
+        m = len(mat)
+        n = len(mat[0])
+
+        re = [0] * m*n
+
+        r, c = 0, 0
+        dir = True
+
+        for i in range(m*n):
+            re[i] = mat[r][c]
+
+            if dir:
+                if r == 0 and c != n-1:
+                    c += 1
+                    dir = False
+                elif c == n-1:
+                    r += 1
+                    dir = False
+                else:
+                    r -= 1
+                    c += 1
+            else:
+                if c == 0 and r != m-1:
+                    r += 1
+                    dir = True
+                elif r == m-1:
+                    c += 1
+                    dir = True
+                else:
+                    r += 1
+                    c -= 1
+
+        return re

Problem3.py

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+# https://leetcode.com/problems/spiral-matrix/description/
+
+class Solution:
+    def spiralOrder(self, matrix: List[List[int]]) -> List[int]:
+
+        m = len(matrix)
+        n = len(matrix[0])
+
+        top = 0
+        bottom = m - 1
+        left = 0
+        right = n - 1
+
+        re = [] 
+
+        while top <= bottom and left <= right:
+
+            for i in range(left, right+1):
+                re.append(matrix[top][i])
+            top += 1
+
+            if top <= bottom and left <= right:
+                for i in range(top, bottom+1):
+                    re.append(matrix[i][right])
+                right -= 1
+
+            if top <= bottom and left <= right:
+                for i in range(right, left-1, -1):
+                    re.append(matrix[bottom][i])
+                bottom -= 1
+
+            if top <= bottom and left <= right:
+                for i in range(bottom, top-1, -1):
+                    re.append(matrix[i][left])
+                left += 1
+
+        return re