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MergeBU.java
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40 lines (37 loc) · 1.01 KB
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package com.mytest.algorithm.sort;
import com.mytest.algorithm.util.Util;
/**
*
* @author wangyujiang
* 自顶向上的归并排序
* 多次遍历整个数组，根据整个数组大小进行两两归并
*/
public class MergeBU {
//原地归并
public static void merge(Comparable[] a, int lo, int mid, int hi) {
int i = lo, j = mid+1;
Comparable[] aux = new Comparable[a.length];
for(int k = lo; k <= hi; k++) {//复制数组
aux[k] = a[k];
}
for(int k = lo; k <= hi; k++) {
if(i>mid) {//左半边用尽
a[k] = aux[j++];
} else if(j>hi) {//右半边用尽
a[k] = aux[i++];
} else if(Util.less(aux[i], aux[j])) {
a[k] = aux[i++];
} else{
a[k] = aux[j++];
}
}
}
public static void sort(Comparable[] a){
int N = a.length;
for(int sz = 1; sz < N; sz = sz+sz) {//进行每一轮归并，下一轮子数组的大小会翻倍
for(int lo = 0; lo < N-sz; lo += sz+sz) { //确定归并子数组lo的位置
merge(a, lo, lo+sz-1, lo+sz+sz-1);//进行归并
}
}
}
}