Day14 - Merge-sorted-array, Remove-duplicates-from-sorted-array-ii , Search-a-2d-matrix-ii

Merge-sorted-array.java

@@ -0,0 +1,24 @@
+class Solution {
+    public void merge(int[] nums1, int m, int[] nums2, int n) {
+        int p1 = m-1;
+        int p2 = n-1;
+        int p3 = m+n-1;
+        while(p1>=0 && p2>=0){
+            if(nums1[p1] <= nums2[p2]){
+                nums1[p3] = nums2[p2];
+                p2--;
+                p3--;
+            }else {
+                nums1[p3] = nums1[p1];
+                p1--;
+                p3--;
+            }
+        }
+
+        while(p2>=0){
+            nums1[p3] = nums2[p2];
+            p2--;
+            p3--;
+        }
+    }
+}

README.md

@@ -1,10 +1,16 @@
 # Two-Pointers-2
 
 ## Problem1 (https://leetcode.com/problems/remove-duplicates-from-sorted-array-ii/)
+* Brutforce - Hasshmap freq map, keep 2 elements
+* Optimal - no extra space used. keep 2 ptrs- i for iterating array, slow ptr for keeping the freq count <=2.
 
 
 ## Problem2 (https://leetcode.com/problems/merge-sorted-array/)
+* Brutforce - Copy nums2 arr behind nums1 arr & then sort it - T(n) = O(m+n log(m+n))
+* Optimal - 3 pointers p1 for nums1 at m-1, p2 for nums2 at n-1, p3 for num1 at m+n-1.
+* comparing p1 & p2 whichever is greater keeping at p3. Look for condition where p2 will still be inbound that time copy elements from p2 to nums1 array at p3.
 
 
 ## Problem3 (https://leetcode.com/problems/search-a-2d-matrix-ii/)
-
+* Top Right or Bottom Left elements have deciding factor - whether to go up/down or left/right.
+* Search the target within limits.

Remove-duplicates-from-sorted-array-ii.java

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+class Solution {
+    public int removeDuplicates(int[] nums) {
+        int count = 1;
+        int slow = 1;
+        for(int i=1;i<nums.length;i++){
+            if(nums[i]==nums[i-1]){
+                count++;
+            }else{
+                count=1;//reset
+            }
+            if(count<=2){
+                nums[slow] = nums[i];
+                slow++;
+            }
+        }
+        return slow;
+    }
+}

Search-a-2d-matrix-ii.java

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+class Solution {
+    public boolean searchMatrix(int[][] matrix, int target) {
+        int m = matrix.length;
+        int n = matrix[0].length;
+        //top right element has deciding power
+        int r = 0, c=n-1;
+        while(r<m && c>=0){
+            if(matrix[r][c] == target) {
+                return true;
+            }else if(matrix[r][c] < target){
+                r++;
+            }else{
+                c--;
+            }
+        }
+
+        return false;
+    }
+}