Solved two pointers

3-sum.java

@@ -0,0 +1,41 @@
+class Solution {
+    public List<List<Integer>> threeSum(int[] nums) {
+        int n = nums.length;
+        List<List<Integer>> result = new ArrayList<>();
+        Arrays.sort(nums); //nlogn
+
+
+        for (int i = 0; i < n; i++) { //O(n^2)
+            //outer duplicacy
+            if (nums[i] > 0)
+                break;
+            if (i > 0 && nums[i] == nums[i - 1])
+                continue;
+            int left = i + 1;
+            int right = n - 1;
+            while (left < right) {
+                int curr = nums[i] + nums[left] + nums[right];
+
+                if (curr == 0) {
+                    result.add(Arrays.asList(nums[i], nums[left], nums[right]));
+                    left++;
+                    right--;
+                    //inner duplicacy
+                    while (left < right && nums[left] == nums[left - 1])
+                        left++;
+                    while (left < right && nums[right] == nums[right + 1])
+                        right--;
+                } else if (curr > 0) {
+                    right--;
+                } else {
+                    left++;
+                }
+            }
+
+        }
+        return new ArrayList<>(result);
+    }
+}
+
+//TC: O(n^2)
+//SC: O(1)

container-max-water.java

@@ -0,0 +1,21 @@
+class Solution {
+    public int maxArea(int[] height) {
+        int p1 = 0;
+        int p2 = height.length - 1;
+        int max = 0;
+
+        while (p1 < p2) {
+            if (height[p1] <= height[p2]) {
+                max = Math.max(max, height[p1] * (p2-p1));
+                p1++;
+            } else {
+                max = Math.max(max, height[p2] * (p2-p1));
+                p2--;
+            }
+        }
+        return max;
+    }
+}
+
+//tc: 0(logn)
+//sc:O(1)

sort-colors.java

@@ -0,0 +1,30 @@
+class Solution {
+    public void sortColors(int[] nums) {
+        int high = nums.length - 1;
+        int low = 0;
+        int mid = 0;
+
+        while (mid <= high) {
+            if (nums[mid] == 2) {
+                swap(nums, mid, high);
+                high--;
+
+            } else if (nums[mid] == 0) {
+                swap(nums, mid, low);
+                low++;
+                mid++;
+            } else {
+                mid++;
+            }
+        }
+    }
+
+    private void swap(int[] nums, int mid, int loh) {
+        int temp = nums[loh];
+        nums[loh] = nums[mid];
+        nums[mid] = temp;
+    }
+}
+
+//TC:O(n)
+//SC: O(1)