归并排序——紫书

最新推荐文章于 2025-12-20 17:21:30 发布

原创最新推荐文章于 2025-12-20 17:21:30 发布 · 166 阅读

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#算法 #数据结构

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归并排序

#include<cstdio>
const int MAXN=200005;
int n, a[MAXN], temp[MAXN];
long long ans;
void count(int l, int r) {
	if(r == l) return ;//结束条件
	int m = (l + r) >> 1;
	count(l, m);
	count(m + 1, r);//二分查找
	int i = l, j = m + 1, k = l;
	while(j <= r || i <= m)    {
		if(j > r || (i <= m && a[i] < a[j]))
			temp[k++] = a[i++];
		else
			temp[k++] = a[j++];
	}
	for(i = l; i <= r; i++) a[i] = temp[i];
}
int main() {
	scanf("%d", &n);
	for(int i = 1; i <= n; i++)
		scanf("%d", &a[i]);
	for(int i = 1; i <= n; i++)
		printf("%d ", a[i]);	
	return 0;
}

逆序对

#include<cstdio>
const int MAXN=200005;
int n, a[MAXN], temp[MAXN];
long long ans;
void count(int l, int r) {
	if(r == l) return ;//结束条件
	int m = (l + r) >> 1;
	count(l, m);
	count(m + 1, r);//二分查找
	int i = l, j = m + 1, k = l;
	while(j <= r || i <= m)    {
		if(j > r || (i <= m && a[i] < a[j]))
			temp[k++] = a[i++];
		else
			temp[k++] = a[j++], ans += m - i + 1;
	}
	for(i = l; i <= r; i++)  a[i] = temp[i];
}
int main() {
	scanf("%d", &n);
	for(int i = 1; i <= n; i++)
		scanf("%d", &a[i]);
	count(1, n);//调用函数
	printf("%lld", ans);//输出
	return 0;
}