Complete Two-Pointers-1

Problem34.java

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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
+
+
+// Your code here along with comments explaining your approach
+class Solution {
+    public void sortColors(int[] nums) {
+        int low = 0; int mid = 0; int high = nums.length-1;
+
+        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 x, int y) {
+        int temp = nums[x];
+        nums[x] = nums[y];
+        nums[y] = temp;
+    }
+}

Problem35.java

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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
+
+
+// Your code here along with comments explaining your approach
+class Solution {
+    public List<List<Integer>> threeSum(int[] nums) {
+        Arrays.sort(nums);
+        int n = nums.length;
+        List<List<Integer>> result = new ArrayList<>();
+
+        for (int i = 0; i < n; i++) {
+            if (i != 0 && nums[i] == nums[i-1]) continue;
+            if (nums[0] > 0) break;
+
+            int low = i+1; int high = n-1;
+
+            while(low < high) {
+                int sum = nums[i] + nums[low] + nums[high];
+                if (sum == 0) {
+                    result.add(Arrays.asList(nums[i], nums[low], nums[high]));
+                    low++;
+                    high--;
+                    while(low < high && nums[low] == nums[low-1]) low++;
+                    while(low < high && nums[high] == nums[high+1]) high--;
+                } else if (sum > 0) {
+                    high--;
+                } else {
+                    low++;
+                }
+            }
+        }
+
+        return result;
+    }
+}

Problem36.java

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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
+
+
+// Your code here along with comments explaining your approach
+class Solution {
+    public int maxArea(int[] height) {
+        int n = height.length;
+
+        int low = 0; int high = n-1;
+        int area = 0;
+
+        while(low < high) {
+            int h = 0;
+            int w = high - low;
+
+            if (height[low] < height[high]) {
+                h = height[low];
+                low++;
+            } else {
+                h = height[high];
+                high--;
+            }
+
+            area = Math.max(area, h*w);
+        }
+
+        return area;
+    }
+}