debug案例

来源：互联网发布：mysql count用法编辑：程序博客网时间：2024/05/22 11:47

有bug的代码：

#include<iostream>#include<cstdio>#include<cstring>#include<algorithm>using namespace std;const int MAXN = 1e5+5;int tree[30][MAXN];int sorted[MAXN];int toleft[30][MAXN];void build(int l,int r,int dep){    if(l==r) return;    int mid=(l+r)>>1;    int same=mid-l+1;    for(int i=l;i<=r;i++)        if(tree[dep][i]<sorted[mid])        same--;    int lpos=l;    int rpos=mid+1;    for(int i=l;i<=r;i++)    {        if(tree[dep][i]<sorted[mid])        {            tree[dep+1][lpos++]=tree[dep][i];        }else if(tree[dep][i]==sorted[mid]&&same>0)        {            tree[dep+1][lpos++]=tree[dep][i];            same--;        }else        {            tree[dep+1][rpos++]=tree[dep][i];        }        toleft[dep][i]=toleft[dep][l-1]+lpos-1;    }    build(l,mid,dep+1);    build(mid+1,r,dep+1);}int query(int L,int R,int l,int r,int dep,int k){    if(l==r) return tree[dep][l];    int mid=(L+R)>>1;    int cnt=toleft[dep][r]-toleft[dep][l-1];    if(cnt>=k)    {        int newl=L+toleft[dep][l-1]-toleft[dep][L-1];        int newr=newl+cnt-1;        return query(L,mid,newl,newr,dep+1,k);    }else    {        int newr=r+toleft[dep][R]-toleft[dep][r];        int newl=newr-(r-l-cnt);        return query(mid+1,R,newl,newr,dep+1,k-cnt);    }}int main(){    int n,m;    while(scanf("%d%d",&n,&m)!=EOF)    {        for(int i=1;i<=n;++i)        {            scanf("%d",&tree[0][i]);            sorted[i]=tree[0][i];        }        sort(sorted+1,sorted+n+1);        build(1,n,0);        while(m--)        {            int a,b,c;            scanf("%d%d%d",&a,&b,&c);            printf("%d\n",query(1,n,a,b,0,c));        }    }    return 0;}/*7 31 5 2 6 3 7 42 5 34 4 11 7 3*/

正确代码：

#include<iostream>#include<cstdio>#include<cstring>#include<algorithm>using namespace std;const int MAXN = 1e5+5;int tree[30][MAXN];int sorted[MAXN];int toleft[30][MAXN];void build(int l,int r,int dep){    if(l==r) return;    int mid=(l+r)>>1;    int same=mid-l+1;    for(int i=l;i<=r;i++)        if(tree[dep][i]<sorted[mid])        same--;    int lpos=l;    int rpos=mid+1;    for(int i=l;i<=r;i++)    {        if(tree[dep][i]<sorted[mid])        {            tree[dep+1][lpos++]=tree[dep][i];        }else if(tree[dep][i]==sorted[mid]&&same>0)        {            tree[dep+1][lpos++]=tree[dep][i];            same--;        }else        {            tree[dep+1][rpos++]=tree[dep][i];        }        toleft[dep][i]=toleft[dep][l-1]+lpos-l;///!    }    build(l,mid,dep+1);    build(mid+1,r,dep+1);}int query(int L,int R,int l,int r,int dep,int k){    if(l==r) return tree[dep][l];    int mid=(L+R)>>1;    int cnt=toleft[dep][r]-toleft[dep][l-1];    if(cnt>=k)    {        int newl=L+toleft[dep][l-1]-toleft[dep][L-1];        int newr=newl+cnt-1;        return query(L,mid,newl,newr,dep+1,k);    }else    {        int newr=r+toleft[dep][R]-toleft[dep][r];        int newl=newr-(r-l-cnt);        return query(mid+1,R,newl,newr,dep+1,k-cnt);    }}int main(){    int n,m;    while(scanf("%d%d",&n,&m)!=EOF)    {        for(int i=1;i<=n;++i)        {            scanf("%d",&tree[0][i]);            sorted[i]=tree[0][i];        }        sort(sorted+1,sorted+n+1);        build(1,n,0);        while(m--)        {            int a,b,c;            scanf("%d%d%d",&a,&b,&c);            printf("%d\n",query(1,n,a,b,0,c));        }    }    return 0;}/*7 31 5 2 6 3 7 42 5 34 4 11 7 3*/

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