solves #2824: Count Pairs Whose Sum is Less than Target in java

Author: anishLearnsToCode

README.txt

@@ -845,5 +845,5 @@
 | 2806 | [Account Balance After Rounded Purchase](https://leetcode.com/problems/account-balance-after-rounded-purchase)                                                         |                                                                                   [![Java](assets/java.png)](src/AccountBalanceAfterRoundedPurchase.java)                                                                                                                                               |                                                                                                                                   |
 | 2810 | [Faulty Keyboard](https://leetcode.com/problems/faulty-keyboard)                                                                                                       |                                                                                   [![Java](assets/java.png)](src/FaultyKeyboard.java)                                                                                                                                               |                                                                                                                                   |
 | 2815 | [Max Pair Sum in an Array](https://leetcode.com/problems/max-pair-sum-in-an-array)                                                                                     |                                                                                   [![Java](assets/java.png)](src/MaxPairSumInAnArray.java)                                                                                                                                               |                                                                                                                                   |
-| 2824 | [Count Pairs Whose Sum is Less than Target](https://leetcode.com/problems/count-pairs-whose-sum-is-less-than-target)                                                   |                                                                                   [![Java](assets/java.png)](src/)                                                                                                                                               |                                                                                                                                   |
+| 2824 | [Count Pairs Whose Sum is Less than Target](https://leetcode.com/problems/count-pairs-whose-sum-is-less-than-target)                                                   |                                                                                   [![Java](assets/java.png)](src/CountPairsWhoseSumIsLessThanTarget.java)                                                                                                                                               |                                                                                                                                   |
 | 2828 | [Check if a String Is an Acronym of Words](https://leetcode.com/problems/check-if-a-string-is-an-acronym-of-words)                                                     |                                                                                   [![Java](assets/java.png)](src/)                                                                                                                                               |                                                                                                                                   |

src/CountPairsWhoseSumIsLessThanTarget.java

@@ -0,0 +1,21 @@
+// https://leetcode.com/problems/count-pairs-whose-sum-is-less-than-target/description
+// T: O(NlogN)
+// S: O(logN)
+
+import java.util.List;
+
+public class CountPairsWhoseSumIsLessThanTarget {
+    public int countPairs(List<Integer> nums, int target) {
+        int pairs = 0;
+        nums.sort(Integer::compareTo);
+        for (int i = 0, j = nums.size() - 1 ; i < j ; ) {
+            if (nums.get(i) + nums.get(j) < target) {
+                pairs += j - i;
+                i++;
+            } else {
+                j--;
+            }
+        }
+        return pairs;
+    }
+}