LA 3938 "Ray, Pass me the dishes!"

题目："Ray, Pass me the dishes!"

思路：线段树。

代码：

#include <cstdio>#include <iostream>#include <algorithm>#include <stack>#include <queue>#include <deque>#include <set>#include <cstring>#include <map>using namespace std;#define ll long long#define maxn 500000struct Pair {int x,y;Pair() {}Pair(int x_,int y_) {x=x_,y=y_;}bool operator <(const Pair& other) const {return x<other.x||(x==other.x&&y<other.y)?true:false;}};int n,m;ll a[maxn+5];//前缀和 Pair maxsub[2*maxn+5];//最大连续和 int maxpre[2*maxn+5],maxsuf[2*maxn+5];//最大前缀、后缀int X,Y;Pair cmp(Pair x1,Pair x2) {//比较x1，x2那段更优 ll y1=a[x1.y]-a[x1.x-1],y2=a[x2.y]-a[x2.x-1];if(y1>y2) return x1;//值的大小 if(y1==y2&&x1<x2) return x1;//坐标的大小 return x2;}void buildtree(int o,int L,int R) {if(L==R) {//叶子节点 maxsub[o]=Pair(L,R);maxpre[o]=maxsuf[o]=L;return ;}int lson=o*2,rson=o*2+1;int mid=(L+R)/2;buildtree(lson,L,mid);buildtree(rson,mid+1,R);if(a[maxpre[lson]]>=a[maxpre[rson]]) maxpre[o]=maxpre[lson];else maxpre[o]=maxpre[rson];if(a[maxsuf[lson]-1]<=a[maxsuf[rson]-1]) maxsuf[o]=maxsuf[lson];//即a[R]-a[maxsuf[lson]-1]>=a[R]-a[maxsuf[rson]-1]else maxsuf[o]=maxsuf[rson];maxsub[o]=cmp(Pair(maxsuf[lson],maxpre[rson]),cmp(maxsub[lson],maxsub[rson]));}Pair qpre(int o,int L,int R) {//前缀最大值 if(maxpre[o]<=Y) return Pair(L,maxpre[o]);//最大前缀被所求区间涵盖 int mid=(L+R)/2;int lson=2*o,rson=2*o+1;if(Y<=mid) return qpre(lson,L,mid);//只在左边 Pair x=qpre(rson,mid+1,R);x.x=L;return cmp(x,Pair(L,maxpre[lson]));}Pair qsuf(int o,int L,int R) {//后缀最大值 if(maxsuf[o]>=X) return Pair(maxsuf[o],R);int mid=(L+R)/2;int lson=2*o,rson=2*o+1;if(X>mid) return qsuf(rson,mid+1,R);Pair x=qsuf(lson,L,mid);x.y=R;return cmp(x,Pair(maxsuf[rson],R));}Pair query(int o,int L,int R) {if(X<=L&&Y>=R) return maxsub[o];int lson=o*2,rson=o*2+1;int mid=(L+R)/2;if(Y<=mid) return query(lson,L,mid);//全左 if(X>mid) return query(rson,mid+1,R);//全右 Pair b=Pair(qsuf(lson,L,mid).x,qpre(rson,mid+1,R).y);//左右各一半 Pair c=query(lson,L,mid),d=query(rson,mid+1,R);//有时，完全在一边的一段比左右各一半的一段更大 return cmp(b,cmp(c,d));}int main() {int T=0;while(~scanf("%d%d",&n,&m)) {for(int i=1; i<=n; i++) {int x;scanf("%d",&x);a[i]=a[i-1]+x;}buildtree(1,1,n);printf("Case %d:\n",++T);for(int i=1; i<=m; i++) {scanf("%d%d",&X,&Y);if(X>Y) swap(X,Y);Pair ans=query(1,1,n);printf("%d %d\n",ans.x,ans.y);}}return 0;}