two pointers 1

container-most-water.py

@@ -0,0 +1,17 @@
+# O(n) time, O(1) space
+
+# move pointers inward when height is lower 
+class Solution:
+    def maxArea(self, height: List[int]) -> int:
+        l=0
+        r=len(height)-1
+        area = 0
+        while l < r:
+            width = r - l
+            if height[l]<=height[r]:
+                area = max(area,height[l]*width)
+                l+=1
+            elif height[l]>height[r]:
+                area = max(area,height[r]*width)
+                r-=1
+        return area

sort-colors.py

@@ -0,0 +1,22 @@
+
+# o(n) time, o(1) space 
+class Solution:
+    def sortColors(self, nums: List[int]) -> None:
+
+        mid = 0
+        low = 0
+        high = len(nums)-1
+
+        while mid <= high:
+
+            if nums[mid] == 2:
+                nums[mid],nums[high] = nums[high],nums[mid]
+                high-=1
+            elif nums[mid] == 0:
+                nums[mid],nums[low]=nums[low],nums[mid]
+                mid+=1
+                low+=1
+            else:
+                mid+=1
+
+        return nums

three-sum.py

@@ -0,0 +1,27 @@
+# time O(n^2), space O(1)
+class Solution:
+    def threeSum(self, nums: list[int]) -> list[list[int]]:
+
+        res=[]
+        for i in range(len(nums)):
+            #outside duplicacy
+            if i != 0 and nums[i] == nums[i-1]:
+                continue
+            a = nums[i]
+            l=i+1
+            r=len(nums)-1
+            while l < r:
+                three = a+nums[l]+nums[r]
+                if three > 0:
+                    dp = nums[r]
+                    while nums[r] == dp and r > l:
+                        r-=1
+                else: 
+                    if three == 0:
+                        res.append([nums[i],nums[l],nums[r]])
+                    # if three less than 0 or three == 0, move left pointer
+                    dup = nums[l]
+                    while nums[l] == dup and l < r:
+                        l+=1
+
+        return res