Completed Competitive_Coding-3

K-diffPairsinanArray.java

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+// Time Complexity : O(n)
+// Space Complexity : O(n)
+// 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
+/*
+Have a map and feed all the values from the array into the map along with their occurences. Now, iterate the
+map and check if the sum of key and k already exists in the map, if so, increment the count. If k is 0,
+then we need to specially check if the value is greater than 1, it means, we can get k by the difference
+of those multiple occurences of that element itself, so increment the count again.
+ */
+class Solution {
+    public int findPairs(int[] nums, int k) {
+        Map<Integer, Integer> map = new HashMap<>();
+        int count = 0;
+        for(int num : nums) {
+            map.put(num, map.getOrDefault(num, 0) + 1);
+        }
+        for(Map.Entry<Integer, Integer> entry : map.entrySet()) {
+            int key = entry.getKey();
+            int val = entry.getValue();
+            if(k > 0 &&map.containsKey(key + k))
+                count++;
+            else if(k == 0 && val > 1)
+                count++;
+        }
+        return count;
+    }
+}

PascalsTriangle.java

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+// Time Complexity : O(n^2)
+// Space Complexity : O(n^2)
+// 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
+/*
+The idea is to append two 1's by default(except for 0th index) to the resultant sublist and compute the
+middle elements by retrieving previous iteration's generated list and add the consecutive elements from
+indices 1 to i - 1 where i needs to iterate for given numRows value. As we compute this sum, append it to
+the subList and add it to the resultant list.
+ */
+class Solution {
+    public List<List<Integer>> generate(int numRows) {
+        List<List<Integer>> result = new ArrayList<>();
+        for(int i = 0 ; i < numRows ; i++) {
+            List<Integer> pascalList = new ArrayList<>();
+            pascalList.add(1);
+            if(i == 0) {
+                result.add(pascalList);
+                continue;
+            }
+            for(int j = 1 ; j <= i - 1 ; j++) {
+                List<Integer> prevList = result.get(i - 1);
+                int sum = prevList.get(j - 1) + prevList.get(j);
+                pascalList.add(sum);
+            }
+            pascalList.add(1);
+            result.add(pascalList);
+        }
+        return result;
+    }
+}