HDU

HDU - 1754 http://acm.hdu.edu.cn/showproblem.php?pid=1754
思路：单点更新+区间查询

#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>using namespace std;const int inf = 0x3f3f3f3f;const int maxn = 200000+10;int n,m;struct node{    int v;    int l,r;    node(int a,int b = -1,int c = -1)    {   v = a; l = b; r = c;    }    node(){}}segtree[maxn << 2];int data[maxn];int bulid_tree(int l,int r,int id){    segtree[id].l = l, segtree[id].r = r;    if(l == r)  {segtree[id].v = data[l]; return data[l];}    int mid = (l+r) >> 1;    int a = bulid_tree(l,mid,id<<1);    int b = bulid_tree(mid+1,r,id<<1|1);    return segtree[id].v = max(a,b);}int updata(int i,int v,int id){    int l = segtree[id].l, r = segtree[id].r;    if(l == r && r == i)    {segtree[id].v = v; return v;}    if(r < i || l > i) return 0;    int mid = (l+r)>>1;    if(mid < i) updata(i,v,id<<1|1);    else updata(i,v,id<<1);    return segtree[id].v = max(segtree[id<<1].v,segtree[id<<1|1].v);}int query(int ql,int qr,int id){    int l = segtree[id].l, r = segtree[id].r;    if(l == ql && r == qr) return segtree[id].v;    if(r < ql || l > ql) return 0;    int mid = l+r>>1;    int ans = 0;    if(qr <= mid)        ans = query(ql,qr,id<<1);    else if(ql > mid)        ans = query(ql,qr,id<<1|1);    else        ans = max(query(ql,mid,id<<1),query(mid+1,qr,id<<1|1));    return ans;}int main(){    while(~scanf("%d%d",&n,&m))    {        for(int i = 1; i <= n ; i++)            scanf("%d",&data[i]);        bulid_tree(1,n,1);        //cout<<"yes"<<endl;        for(int i = 0; i < m ; i++)        {            char s[5];            int a,b;            scanf("%s%d%d",s,&a,&b);            if(s[0] == 'Q')                printf("%d\n",query(a,b,1));            else                updata(a,b,1);        }    }    return 0;}

//树状数组代码，但是这个未能理解，参考了别人的代码

#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>using namespace std;const int maxn = 200000+10;int n,m;int a[maxn],b[maxn];int lowbit(int x){   return x & -x;  }void updata(int x){    int lx,i;    for(; x <= n; x += lowbit(x))    {        b[x] = a[x];        lx = lowbit(x);        for(i = 1; i < lx; i = (i<<1))            b[x] = max(b[x],b[x-i]);    }}int query(int x,int y){    int ans = 0;    while(x <= y)    {        ans = max(a[y--],ans);        for(; y - lowbit(y) >= x; y -= lowbit(y))            ans = max(ans, b[y]);    }    return ans;}int main(){    while(~scanf("%d%d",&n,&m))    {        for(int i = 1; i <= n ; i++) scanf("%d",&a[i]), updata(i);        for(int i = 0; i < m ; i++)        {            char s[5]; int x,y;            scanf("%s%d%d",s,&x,&y);            if(s[0] == 'U') a[x] = y,updata(x);            else printf("%d\n",query(x,y));        }    }    return 0;}