/*
 * copyright 2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and 
 * limitations under the License.
*/
package top.pengcheng789.algorithms.sort

import java.util.*

/**
 *
 * @author <NAME>
 */
class LoopQuickSort<T: Comparable<T>>: Sort<T> {

    override fun sort(list: MutableList<T>) {
        if (list.isEmpty()) {
            return
        }

        val stack = Stack<Array<Int>>()
        stack.push(arrayOf(0, list.size - 1))

        do {
            val range = stack.pop()
            val pivotIndex = (range[0] + range[1]) shr 1
            val pivotNewIndex = partition(list, range[0], range[1], pivotIndex)

            if (range[0] < pivotNewIndex - 1) {
                stack.push(arrayOf(range[0], pivotNewIndex - 1))
            }
            if (range[1] > pivotNewIndex + 1) {
                stack.push(arrayOf(pivotNewIndex + 1, range[1]))
            }
        } while (stack.isNotEmpty())
    }

    private fun partition(list: MutableList<T>, left: Int,
                          right: Int, pivotIndex: Int): Int {
        val pivotValue = list[pivotIndex]
        swap(list, right, pivotIndex)
        var storeIndex = left

        var i = left
        while (i < right) {
            if (list[i] <= pivotValue) {
                swap(list, i, storeIndex)
                storeIndex++
            }
            i++
        }

        swap(list, storeIndex, right)
        return storeIndex
    }
}
