Done Array-1

Problem1.java

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+//Time Complexity : O(n)
+//Space Complexity : O(1)  // output array not counted
+//Did this code successfully run on Leetcode : Yes
+//First, we create a result list where each position will store the final answer.
+
+//Then we do a left pass: for every index, we multiply all numbers to its left and store that in result.
+
+//Next, we do a right pass: we multiply everything to its right and add it to the result.
+
+//Combining left × right gives the final answer for each position without using division.
+class Solution {
+    public int[] productExceptSelf(int[] nums) {
+
+        int n = nums.length;
+        int[] result = new int[n];
+
+        // LEFT PASS
+        result[0] = 1;
+        for (int i = 1; i < n; i++) {
+            result[i] = result[i - 1] * nums[i - 1];
+        }
+
+        // RIGHT PASS
+        int rightProduct = 1;
+        for (int i = n - 1; i >= 0; i--) {
+            result[i] = result[i] * rightProduct;
+            rightProduct = rightProduct * nums[i];
+        }
+
+        return result;
+    }
+}
+

Problem2.java

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+//Time Complexity : O(m * n)
+//Space Complexity : O(1)  // excluding the result array
+//Did this code successfully run on Leetcode : Yes
+// We move through the matrix diagonally in two directions: up-right and down-left.
+// Whenever we hit a boundary (top, bottom, left, or right), we switch direction.
+// We keep updating the row and column based on the current direction until all elements are added.
+// This allows us to traverse the entire matrix in the required diagonal zig-zag order.
+class Solution {
+    public int[] findDiagonalOrder(int[][] mat) {
+        int m = mat.length;
+        int n = mat[0].length;
+
+        int[] result = new int[m * n];
+        int r = 0, c = 0;
+        boolean up = true; // true = up-right, false = down-left
+
+        for (int i = 0; i < m * n; i++) {
+
+            result[i] = mat[r][c]; // add current element
+
+            if (up) {  // moving up-right ↗
+
+                if (c == n - 1) {     // hit RIGHT wall
+                    r++;              // move DOWN
+                    up = false;       // change direction
+                } 
+                else if (r == 0) {    // hit TOP wall
+                    c++;              // move RIGHT
+                    up = false;       // change direction
+                }
+                else {                // normal up-right move
+                    r--; 
+                    c++;
+                }
+
+            } else { // moving down-left ↘
+
+                if (r == m - 1) {     // hit BOTTOM wall
+                    c++;              // move RIGHT
+                    up = true;        // change direction
+                }
+                else if (c == 0) {    // hit LEFT wall
+                    r++;              // move DOWN
+                    up = true;        // change direction
+                }
+                else {                // normal down-left move
+                    r++; 
+                    c--;
+                }
+            }
+        }
+
+        return result;
+    }
+}
+

Problem3.java

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+// We maintain four boundaries: top, bottom, left, and right.
+// In each loop, we traverse the matrix in four directions: left→right, top→bottom, right→left, and bottom→top.
+// After completing one spiral layer, we shrink the boundaries inward.
+// We repeat this until all rows and columns are processed in spiral order.
+//Time Complexity : O(m * n)
+//Space Complexity : O(1)  // excluding result list
+//Did this code successfully run on Leetcode : Yes
+class Solution {
+    public List<Integer> spiralOrder(int[][] matrix) {
+        int m = matrix.length;//no. of rows
+        int n = matrix[0].length;//no.of columns
+        int top = 0, bottom = m-1, left = 0, right = n-1;
+        List<Integer> result = new ArrayList<>();
+        while (top <= bottom && left <= right){
+            for (int i = left; i <= right; i++){
+                result.add(matrix[top][i]);
+            }
+            top++;
+
+    for (int i = top; i <= bottom; i++ ){
+        result.add(matrix[i][right]);
+    }
+    right--;
+if (top <= bottom){
+    for(int i = right; i >= left; i--){
+        result.add(matrix[bottom][i]);
+    }
+    bottom--;
+}
+if(left <= right){
+for (int i = bottom; i >= top; i--){
+    result.add(matrix[i][left]);
+
+}
+left++;
+}
+        }
+
+return result;
+}
+}