Submission #434152

#TimeUsernameProblemLanguageResultExecution timeMemory
434152dqhungdlRainforest Jumps (APIO21_jumps)C++17
100 / 100
1635 ms67008 KiB
#include "jumps.h"

#include <bits/stdc++.h>
using namespace std;

typedef pair<int,int> ii;
const int MAX=2e5+5;
int Lg[MAX],J[MAX][20],JR[MAX][20];
ii f[MAX][20];

ii query(int l,int r) {
	int k=Lg[r-l+1];
	return max(f[l][k],f[r-(1<<k)+1][k]);
}

void init(int N, std::vector<int> H) {
	// Init log
	for(int i=1;i<=N;i++)
		Lg[i]=log2(i);
	// Init RMQ
	for(int i=0;i<N;i++)
		f[i][0]=ii(H[i],i);
	for(int k=1;(1<<k)<=N;k++)
		for(int i=0;i+(1<<k)-1<N;i++)
			f[i][k]=max(f[i][k-1],f[i+(1<<(k-1))][k-1]);
	vector<int> L(N),R(N);
	// Init left
	for(int i=0; i<N;i++) {
		int tmp=i-1;
		while(tmp>=0&&H[tmp]<=H[i])
			tmp=L[tmp];
		L[i]=tmp;
	}
	// Init right
	for(int i=N-1; i>=0;i--) {
		int tmp=i+1;
		while(tmp<N&&H[tmp]<=H[i])
			tmp=R[tmp];
		R[i]=tmp;
	}
	// Init jumps RMQ
	for(int i=0;i<N;i++) {
		if(L[i]==-1&&R[i]==N)
			J[i][0]=-1;
		else if(L[i]==-1)
			J[i][0]=R[i];
		else if(R[i]==N)
			J[i][0]=L[i];
		else if(H[L[i]]>H[R[i]])
			J[i][0]=L[i];
		else
			J[i][0]=R[i];
	}
	for(int k=1;k<20;k++)
		for(int i=0;i<N;i++)
			if(J[i][k-1]==-1)
				J[i][k]=-1;
			else
				J[i][k]=J[J[i][k-1]][k-1];
	// Init jumps right RMQ
	for(int i=0;i<N;i++)
		JR[i][0]=R[i];
	for(int k=1;k<20;k++)
		for(int i=0;i<N;i++)
			if(JR[i][k-1]==N)
				JR[i][k]=N;
			else
				JR[i][k]=JR[JR[i][k-1]][k-1];
}

int minimum_jumps(int A, int B, int C, int D) {
	// Special cases
	ii maxCD=query(C,D);
	if(f[B][0].first>=maxCD.first)
		return -1;
	if(B+1==C)
		return 1;
	ii maxBC=query(B+1,C-1);
	if(maxBC.first>=maxCD.first)
		return -1;
	// Find the starting position
	int pos=B;
	for(int i=19;i>=0;i--) {
		if((1<<i)>pos-A||f[pos-(1<<i)][i].first>=maxCD.first)
			continue;
		pos-=(1<<i);
	}
	pos=query(pos,B).second;
	if(f[pos][0].first>=maxBC.first)
		return 1;
	// RMQ jumps
	int rs=0;
	for(int i=19;i>=0;i--) {
		if(J[pos][i]==-1||f[J[pos][i]][0].first>=maxBC.first)
			continue;
		pos=J[pos][i];
		rs+=(1<<i);
	}
	if(J[pos][0]!=-1&&f[J[pos][0]][0].first<maxCD.first)
		return rs+2;
	// RMQ jumps right
	for(int i=19;i>=0;i--)
		if(JR[pos][i]<C) {
			rs+=(1<<i);
			pos=JR[pos][i];
		}
	return rs+1;
}
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