归并排序JAVA实现

最新推荐文章于 2025-08-14 09:11:10 发布

转载最新推荐文章于 2025-08-14 09:11:10 发布 · 415 阅读

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package cn.ahern88.algorithm;

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import java.util.Arrays;

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/**

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 *
 归并排序，从小到大

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 *
 归并排序算法一般需要三步

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 *
 1. 左边排序

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 *
 2. 右边排序

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 *
 3. 合并

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 *
 需要用到递归调用

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 *
 @author ahern88

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 */

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public class MergeSort
 {

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    public int[]
 sort(int[]
 arrs){

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        if(arrs.length
 < 2){

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            return arrs;

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        }

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        int middle
 = arrs.length % 2 == 0 ?
 arrs.length / 2 :
 (arrs.length - 1)
 / 2;

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        int[]
 left = Arrays.copyOfRange(arrs, 0,
 middle);

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        int[]
 right = Arrays.copyOfRange(arrs, middle, arrs.length);

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        int[]
 lres = sort(left);

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        int[]
 rres = sort(right);

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        return merge(lres,
 rres);

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    }

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    private int[]
 merge(int[]
 lres, int[]
 rres) {

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        int[] 
 res = new int[lres.length
 + rres.length];

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        int l
 = 0;

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        int r
 = 0;

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        int c
 = 0;

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        while(l
 < lres.length && r < rres.length){

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            if(lres[l]
 < rres[r]){

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                res[c++]
 = lres[l++];

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            } else {

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                res[c++]
 = rres[r++];

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            }

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        }

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        if(l
 == lres.length){

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            while(r
 < rres.length){

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                res[c++]
 = rres[r++];

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            }

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            return res;

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        }

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        if(r
 == rres.length){

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            while(l
 < lres.length){

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                res[c++]
 = lres[l++];

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            }

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            return res;

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        }

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        return res;

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    }

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}