codeUp 3105 归并排序

最新推荐文章于 2021-03-22 19:28:59 发布

原创最新推荐文章于 2021-03-22 19:28:59 发布 · 178 阅读

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本文深入探讨了归并排序算法的实现细节，包括递归和迭代两种版本，通过代码示例展示了如何对数组进行高效排序。文章涵盖了算法的核心概念、关键步骤及其实现技巧。

#include<cstdio>
#include<cstring>
#include<iostream>
#include<map>
#include<cmath>
#include<algorithm>
#include<set>
#include<vector>
#include<climits>
#define Equal(a,b) (fabs((a)-(b))<=eps)
#define LessEqu(a,b) (((a)-(b))<=eps)
#define Lessthan(a,b) (((a)-(b))<-eps)
#define Morethan(a,b) (((a)-(b))>=eps)
#define MoreEqu(a,b) (((a)-(b))>=-eps)

using namespace std;
typedef long long ll;
const double eps = 1e-5;
const ll mod = 1000000007;
const int maxn = 100010;
int ans[maxn],arr[maxn];
void merge_sort(int l,int r){
    if(l>=r)return;
    int mid = l+(r-l)/2;
    merge_sort(l,mid);
    merge_sort(mid+1,r);
    int a,b,cnt = l;

    for(a=l,b=mid+1;a<=mid&&b<=r;){
        if(arr[a]<=arr[b])
            ans[cnt++] = arr[a],a++;
        else
            ans[cnt++] = arr[b],b++;
    }

    while(a<=mid)ans[cnt++] = arr[a++];
    while(b<=r)ans[cnt++] = arr[b++];

    for(int i=l;i<=r;i++)
        arr[i] = ans[i];

}
int main(){
    int n;
    scanf("%d",&n);
    while(n--){
        int m;
        scanf("%d",&m);
        for(int i=1;i<=m;i++)
            scanf("%d",&arr[i]);

        merge_sort(1,m);
        for(int i=1;i<=m;i++)
            printf("%d%c",ans[i],i==m?'\n':' ');
    }
    return 0;
}

递归版本

#include<cstdio>
#include<cstring>
#include<iostream>
#include<map>
#include<cmath>
#include<algorithm>
#include<set>
#include<vector>
#include<climits>
#define Equal(a,b) (fabs((a)-(b))<=eps)
#define LessEqu(a,b) (((a)-(b))<=eps)
#define Lessthan(a,b) (((a)-(b))<-eps)
#define Morethan(a,b) (((a)-(b))>=eps)
#define MoreEqu(a,b) (((a)-(b))>=-eps)

using namespace std;
typedef long long ll;
const double eps = 1e-5;
const ll mod = 1000000007;
const int maxn = 100010;
int ans[maxn],arr[maxn];
void merge_sort(int l,int mid,int r){
    int a = l,b = mid+1,cnt=l;
    for(;a<=mid&&b<=r;){
        if(arr[a]<=arr[b])
            ans[cnt++] = arr[a++];
        else
            ans[cnt++] = arr[b++];
    }
    while(a<=mid)ans[cnt++] = arr[a++];
    while(b<=r)ans[cnt++] = arr[b++];
    for(int i=l;i<=r;i++)
        arr[i] = ans[i];
}
int main(){
    int n;
    scanf("%d",&n);
    while(n--){
        int m;
        scanf("%d",&m);
        for(int i=1;i<=m;i++)
            scanf("%d",&arr[i]);

        for(int step = 2;step/2<=m;step*=2){
            for(int i=1;i<=m;i+=step){
                int mid = i+step/2-1;
                if(mid<m)
                merge_sort(i,mid,min(i+step-1,m));
            }
        }

        for(int i=1;i<=m;i++)
            printf("%d%c",ans[i],i==m?'\n':' ');
    }
    return 0;
}

迭代