Done Two-Pointers-1

3sum.py

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+''' Time Complexity : O(n^2) 
+    Space Complexity : O(1) 
+    Did this code successfully run on Leetcode : Yes
+    Any problem you faced while coding this :  No
+
+
+   Approach : Fix the 1st number and run 2sum on rest array using TWO - pointers
+'''
+class Solution:
+    def threeSum(self, nums: List[int]) -> List[List[int]]:
+        nums.sort()
+        print(nums)
+        n = len(nums)
+        res = []
+        for i in range(n-1):
+            if i > 0 and nums[i] == nums[i-1]:
+                continue
+            l, r = i+1, n-1
+            while l < r:
+                summ = nums[i] + nums[l] + nums[r]
+                if summ == 0:
+                    res.append([nums[i],nums[l],nums[r]])
+                    l += 1
+                    r -= 1
+                    while l < r and nums[l] == nums[l-1]:
+                        l += 1
+                    while l < r and nums[r] == nums[r+1]:
+                        r -= 1
+                elif summ > 0:
+                    r -= 1
+                else:
+                    l += 1
+        return res
+
+
+

container-with-most-water.py

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+''' Time Complexity : O(n) 
+    Space Complexity : O(1) 
+    Did this code successfully run on Leetcode : Yes
+    Any problem you faced while coding this :  No
+'''
+
+class Solution:
+    def maxArea(self, height: List[int]) -> int:
+        n= len(height)
+        l, r = 0, n-1
+        maxarea = 0
+        while l < r:
+            h = min(height[l],height[r])
+            w = (r - l)
+            area = h * w
+            maxarea = max(maxarea, area)
+            if height[l] < height[r]:
+                l += 1
+            else:
+                r -= 1
+        return maxarea

sort-colors.py

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+''' Time Complexity : O(n) 
+    Space Complexity : O(1) 
+    Did this code successfully run on Leetcode : Yes
+    Any problem you faced while coding this :  No
+
+
+   Approach : Use 3 pointers, 1 for collecting 0, one for collecting 2, and mid to iterate array
+              swap the elements so that, 0s are at left, 2s are at right and 1s are at the middle
+
+'''
+
+class Solution:
+    def sortColors(self, nums: List[int]) -> None:
+        """
+        Do not return anything, modify nums in-place instead.
+        """
+        n = len(nums)
+        l, mid, r = 0, 0 , n-1
+        def swap(nums, x, y):
+            temp = nums[x]
+            nums[x] = nums[y]
+            nums[y] = temp
+
+        while mid <= r:
+            if nums[mid] == 2:
+                swap(nums,mid,r)
+                r -= 1
+            elif nums[mid] == 0:
+                swap(nums,mid,l)
+                l += 1
+                mid += 1
+            else:
+                mid += 1
+