Two Pointers-2 Done

DuplicatesInSortedArray.java

@@ -0,0 +1,38 @@
+// Time Complexity : O(N), touching each element twice O(2N) = ~O(N)
+// Space Complexity : O(1), Updating the array in place
+// Did this code successfully run on Leetcode : Yes
+// Approach :
+
+// We need to identify the count of each value in the array and keep min(count, k) values of that elements.
+// We can keep a count variable to count the frequency, which should be reset before calculating the frequency of the next elements.
+// In order to track which elements needs to be replaced by which value, we can have two pointers starting from same position,
+// but moving at fast and slow pace.
+// The slow pointer indicates the index that needs to be updated and fast pointer indicates the value, the index
+// needs to be updated with.
+public class DuplicatesInSortedArray {
+    public int removeDuplicates(int[] nums) {
+        int len = nums.length;
+        int slow = 0;
+        int fast = 0;
+        int k = 2;
+        while(fast < len){
+            int count = 0;
+            // Keep the value, needed for frequency calculation and replacing the slow pointer value later
+            int currValue = nums[fast];
+            while(fast < len && nums[fast] == currValue) {
+                fast++;
+                count++;
+            }
+            // Repeat value only min( current value count, given value k) times
+            int minHops = Math.min(count, k);
+            while(minHops != 0){
+                //Override the duplicate values with required values of the next element.
+                nums[slow] = currValue;
+                slow++;
+                minHops--;
+            }
+        }
+
+        return slow;
+    }
+}

MergeSortedArray.java

@@ -0,0 +1,35 @@
+// Time Complexity : O(M+N), M and N size of the 2 array
+// Space Complexity : O(1), in-place
+// Did this code successfully run on Leetcode : Yes
+// Approach :
+//
+// We should compare the last values of the two arrays using 2 pointers, whichever is greater, it should be stored at the last value
+// and that pointer should be reduced by 1.
+public class MergeSortedArray {
+
+    public void merge(int[] nums1, int m, int[] nums2, int n) {
+        if(m == 0 && n == 0) return;
+        int len = m+n-1;
+        int p1 = m-1;
+        int p2 = n-1;
+        while(p1 >= 0 && p2 >=0){
+            // Compare the 2 values at last index in the array, copy the greater value to the last index.
+            // Reduce the pointer by 1
+            if(nums1[p1] >= nums2[p2]){
+                nums1[len] = nums1[p1];
+                len--;
+                p1--;
+            }else{
+                nums1[len] = nums2[p2];
+                len--;
+                p2--;
+            }
+        }
+
+        // Take cares of scenario where p1 reaches 0, indicating all values in nums1 array are explored and nums2
+        // array still has some lower values that needs to be explored
+        while(p2 >= 0){
+            nums1[len--] = nums2[p2--];
+        }
+    }
+}

SearchIn2DMatrix.java

@@ -0,0 +1,36 @@
+// Time Complexity : O(M+N), in the worst case, we will traverse the rows and cols in step form,
+// move left, move down, so m rows down, n cols left
+// Space Complexity : O(1), in place search
+// Did this code successfully run on Leetcode : Yes
+// Approach :
+
+// Brute force - search linearly every cell.
+// Optimal - Find a cell which can divide your search space by half (top right corner or bottom left corner)
+// From that cell, compare the target, if the target is greater move to the next row as it is sorted and search in that row.
+// If the target is smaller, move to prev col and search on the left.
+public class SearchIn2DMatrix {
+
+    public boolean searchMatrix(int[][] matrix, int target) {
+        int rows = matrix.length;
+        int cols = matrix[0].length;
+        if(rows == 1 && cols == 1){
+            return matrix[0][0] == target;
+        }
+        // Search from top left corner
+        int startRow = 0;
+        int startCol = cols-1;
+
+
+        while(startRow <= rows-1 && startCol >= 0 ){
+            if(target == matrix[startRow][startCol]) return true;
+            // if target is greater, search in next row as values are sorted by row
+            if(target > matrix[startRow][startCol]){
+                startRow++;
+            }else {
+                // if target is smaller, search on prev col as values are sorted by col too.
+                startCol--;
+            }
+        }
+        return false;
+    }
+}