14级组队赛第一场3317- 反演

来源：互联网发布：图书馆可视化数据工具编辑：程序博客网时间：2024/05/17 04:56

思路：

归并排序然后减去K

CODE

#include<stdio.h>#include<string.h>#include<stdlib.h>#define NN 500004#define NL 1000long long res;int b[NN]; // 中间辅助数组int ls[NN];void copy(int l, int r){    int i;    for(i = l; i <= r; i++)        ls[i] = b[i];}void merge(int l, int mid ,int r){    int i = l;    int j = mid+1;    int k = l;    while(i <= mid && j <= r)    {        if(ls[i] <=ls[j])        {            b[k++] = ls[i];            i++;        }        else        {            b[k++] = ls[j];            j++;            res += mid-i+1;        }    }    while(i <= mid)    {        b[k++] = ls[i];        i++;    }    while(j <= r)    {        b[k++] = ls[j];        j++;    }}void mergesort(int l, int r){    if(l < r)    {        int mid = l+(r-l)/2;        mergesort(l,mid);        mergesort(mid+1,r);        merge(l,mid,r);        copy(l,r);    }}int main(){    int n, k;    while(~scanf("%d%d",&n,&k))    {        int i;        res = 0;        for(i = 1; i <= n; i++)        scanf("%d",&ls[i]);        mergesort(1,n);        res = res - k;        if(res < 0)            res = 0;        printf("%lld\n",res);    }    return 0;}

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