AC https://leetcode-cn.com/problems/shu-zu-zhong-de-ni-xu-dui-lcof

Author: AaronLinRC

src/main/kotlin/leetcode/shu-zu-zhong-de-ni-xu-dui-lcof/Solution.kt

@@ -0,0 +1,58 @@
+package leetcode.`shu-zu-zhong-de-ni-xu-dui-lcof`
+
+import org.junit.Test
+
+// 太难了。。。写得头都要裂了才写出来
+class Solution {
+    companion object {
+        var count = 0
+    }
+
+    fun reversePairs(nums: IntArray): Int {
+        count =0
+        if (nums.isEmpty()) return 0
+        process(0, nums.lastIndex, nums)
+        return count
+    }
+
+    fun process(l: Int, r: Int, nums: IntArray): IntArray {
+        if (!(l in nums.indices && r in nums.indices && l < r)) return intArrayOf(nums[l])
+        val mid = l + ((r - l) shr 2)
+        return merge(process(l, mid, nums), process(mid + 1, r, nums))
+    }
+
+    fun merge(arrayL: IntArray, arrayR: IntArray): IntArray {
+        val merge = IntArray(arrayL.size + arrayR.size)
+        var pL = 0
+        var pR = 0
+        var index = 0
+        while ((pL in arrayL.indices) && (pR in arrayR.indices)) {
+            if (arrayL[pL] <= arrayR[pR]) {
+                merge[index] = arrayL[pL]
+                pL++
+            } else {
+                merge[index] = arrayR[pR]
+                pR++
+                count += (arrayL.size - pL)
+            }
+            index++
+        }
+        while (pL in arrayL.indices) {
+            merge[index] = arrayL[pL]
+            index++
+            pL++
+        }
+        while (pR in arrayR.indices) {
+            merge[index] = arrayR[pR]
+            index++
+            pR++
+        }
+        return merge
+    }
+
+    @Test
+    fun test() {
+        val intArray = intArrayOf(2,4,3,5,1)
+        println( reversePairs(intArray))
+    }
+}