package org.lion.euler.study.sort;

/**
 * 归并排序
 * 原理:两两合并
 * @author lion
 *
 */
public class MergeSort extends AbstractSort {

	@Override
	public void sort(Integer[] array) {
		this.sort(array, 0, array.length - 1);
	}
	
	private void sort(Integer[] array, int begin, int end) {
		int mid = (begin + end ) / 2;
		if( begin < end){
			this.sort(array, begin, mid);
			this.sort(array, mid + 1, end);
			this.merge(array, begin, mid, end);
		}
	}
	
	private void merge(Integer[] array, int begin, int mid, int end){
		Integer[] result = new Integer[end - begin + 1];
		int beginIndex = begin;
		int nextIndex = mid + 1;
		int index = 0;
		while(beginIndex <= mid && nextIndex <= end){
			if(array[beginIndex] < array[nextIndex]){
				result[index++] = array[beginIndex++];
			}else {
				result[index++] = array[nextIndex++];
			}
		}
		while(beginIndex <= mid){
			result[index++] = array[beginIndex++];
		}
		while(nextIndex <= end){
			result[index++] = array[nextIndex++];
		}
		for (int i = 0; i < result.length; i++) {
			array[begin + i] = result[i];
		}
	}

}