StackedQuicksort.java

import java.util.Stack;

public class StackedQuicksort {
    public static void sort(Comparable<?>[] data, int left, int right) {
        Stack<Integer> stack = new Stack<>();
        stack.push(left);
        stack.push(right);
        while (!stack.empty()) {
            right = stack.pop();
            left = stack.pop();
            if (left >= right) continue;
            int pi = partition(data, left, right);
            stack.push(left);
            stack.push(pi - 1);
            stack.push(pi + 1);
            stack.push(right);
        }
    }

    private static int partition(Comparable<?>[] data, int left, int right) {
        int p = right;
        int store = left;
        Comparable val2 = data[p];
        for (int i = left; i < right; i++) {
            Comparable val1 = data[i];
            if (val1.compareTo(val2) <= 0) {
                swap(data, i, store);
                store++;
            }
        }
        swap(data, store, right);
        return store;
    }

    private static void swap(Comparable<?>[] data, int x, int y) {
        Comparable<?> temp = data[x];
        data[x] = data[y];
        data[y] = temp;
    }
}