Create 1512-number-of-good-pairs.kt

Author: a93a

kotlin/1512-number-of-good-pairs.kt

@@ -0,0 +1,51 @@
+// rolling count
+class Solution {
+    fun numIdenticalPairs(nums: IntArray): Int {
+        val count = HashMap<Int, Int>()
+        var total = 0
+
+        for (n in nums) {
+            count[n]?.let {
+                total += it
+            }
+            count[n] = count.getOrDefault(n, 0) + 1
+        }
+
+        return total
+    }
+}
+
+// count and use arithmetic sequence
+class Solution {
+    fun numIdenticalPairs(nums: IntArray): Int {
+        val count = HashMap<Int, Int>().apply {
+            for (n in nums) {
+                this[n] = getOrDefault(n, 0) + 1
+            }
+        }
+
+        var res = 0
+        for (c in count.values) {
+            res += c * (c - 1) / 2
+        }
+        
+        return res
+    }
+}
+
+// brute force
+class Solution {
+    fun numIdenticalPairs(nums: IntArray): Int {
+        var count = 0
+
+        for (i in 0 until nums.size) {
+            for (j in i + 1 until nums.size) {
+                if (nums[i] == nums[j]) {
+                    count++
+                }
+            }
+        }
+
+        return count
+    }
+}