Completed this module

_118_Pascal_Triangle.java

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+/**** Method 1 ****/
+//Time Complexity: O(n^2)
+//Space Complexity: O(n^2)
+
+//Successfully submitted in LeetCode
+
+//Take two loops, start with traversing the arrays, if at the start or end insert 1 or insert sum of both j and j-1 from i-1 index of ans list. At the end return ans.
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class _118_Pascal_Triangle {
+
+  public List<List<Integer>> generate(int numRows) {
+    List<List<Integer>> res = new ArrayList<>();
+
+    for (int i = 0; i < numRows; i++) {
+      List<Integer> list = new ArrayList<>();
+      for (int j = 0; j < i + 1; j++) {
+        if (j == 0 || j == i) {
+          list.add(1);
+        } else {
+          list.add(res.get(i - 1).get(j - 1) + res.get(i - 1).get(j));
+        }
+      }
+      res.add(list);
+    }
+    return res;
+  }
+}

_532_K_diff_Pairs_in_an_Array.java

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+/**** Method 1 ****/
+//Time Complexity: O(n)
+//Space Complexity: O(n)
+
+//Successfully submitted in LeetCode
+
+//As we just need count, we can create a frequency HashMap and traverse to find if i-k is present or not if yes we increase count, in edge case where k is zero, for every entry we increment count if their frequency is greater than two, as they can form a pair. At the end return count.
+
+/**** Method 2 ****/
+//Time Complexity: O(n)
+//Space Complexity: O(n)
+
+//Successfully submitted in LeetCode
+
+//In this solution we try to find all unique pairs and return their count. To find unique pairs, we insert all the values in nums array into a Hashmap with their index, so that we only have unique entries. Next check if pair(val,val-k) and check if map.get(val-k) is not equal to i(This works when k == 0 as we only have unique values) is present or not if yes sort that pair and add it in HashSet<Pair>(to avoid duplicates), do the same with pair(val,val+k).
+
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+
+/**** Method 1 ****/
+public class _532_K_diff_Pairs_in_an_Array {
+
+  public int findPairs(int[] nums, int k) {
+    int ans = 0;
+
+    HashMap<Integer, Integer> map = new HashMap();
+
+    for (int i : nums) {
+      map.put(i, map.getOrDefault(i, 0) + 1);
+    }
+
+    for (int num : map.keySet()) {
+      int frq = map.get(num);
+      if (k == 0) {
+        if (frq >= 2) {
+          ans++;
+        }
+      } else {
+        if (map.containsKey(num - k)) {
+          ans++;
+        }
+      }
+    }
+
+    return ans;
+  }
+
+  /**** Method 2 ****/
+  public int findPairs1(int[] nums, int k) {
+    HashMap<Integer, Integer> map = new HashMap<>();
+
+    for (int i = 0; i < nums.length; i++) {
+      map.put(nums[i], i);
+    }
+
+    HashSet<List<Integer>> entryHashSet = new HashSet<>();
+
+    for (int i = 0; i < nums.length; i++) {
+      if (map.containsKey(nums[i] - k) && map.get(nums[i] - k) != i) {
+        Integer[] arr = { nums[i], nums[i] - k };
+        Arrays.sort(arr);
+
+        entryHashSet.add(Arrays.asList(arr));
+      }
+
+      if (map.containsKey(nums[i] + k) && map.get(nums[i] + k) != i) {
+        Integer[] arr = { nums[i], nums[i] + k };
+        Arrays.sort(arr);
+
+        entryHashSet.add(Arrays.asList(arr));
+      }
+    }
+
+    return entryHashSet.size();
+  }
+}