Submission #814767

#	Time	Username	Problem	Language	Result	Execution time	Memory
814767		sentheta	Rainforest Jumps (APIO21_jumps)	C++17	100 / 100	1225 ms	50568 KiB

jumps

#include "jumps.h"

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

constexpr int kMaxLogN = 20;

int N;
vector<int> H;
vector<vector<int>> L, R;
vector<vector<int>> higher;

void init(int _N, std::vector<int> _H) {
	N = _N;
	H = _H;

	H.insert(H.begin(), INT_MAX);
	H.insert(H.end(), INT_MAX);
	N += 2;
	L = R = higher = vector<vector<int>>(kMaxLogN, vector<int>(N));
	
	// leftward edges
	stack<int> stak;
	for (int i = 0; i < N; ++i) {
		while (!stak.empty() && H[stak.top()] <= H[i]) {
			stak.pop();
		}
		L[0][i] = stak.empty() ? i : stak.top();
		stak.push(i);
	}

	// rightward edges
	while (!stak.empty()) {
		stak.pop();
	}
	for (int i = N - 1; i >= 0; --i) {
		while (!stak.empty() && H[stak.top()] <= H[i]) {
			stak.pop();
		}
		R[0][i] = stak.empty() ? i : stak.top();
		stak.push(i);
	}

	for (int i = 0; i < N; ++i) {
		higher[0][i] = H[L[0][i]] > H[R[0][i]] ? L[0][i] : R[0][i];
	}

	for (int j = 1; j < kMaxLogN; ++j) {
		for (int i = 0; i < N; ++i) {
			L[j][i] = L[j - 1][L[j - 1][i]];
			R[j][i] = R[j - 1][R[j - 1][i]];
			higher[j][i] = higher[j - 1][higher[j - 1][i]];
		}
	}
}

int maximum_height_index(int l, int r) {
	for (int j = kMaxLogN - 1; j >= 0; --j) {
		if (R[j][l] <= r) {
			l = R[j][l];
		}
	}
	return l;
}

int minimum_jumps(int A, int B, int C, int D) {
	++A; ++B; ++C; ++D;
	// touching
	if (B == C - 1) {
		return R[0][B] <= D ? 1 : -1;
	}
	
	int m = maximum_height_index(B + 1, C - 1);
	// jump over
	if (H[B] > H[m]) {
		return R[0][B] <= D ? 1 : -1;
	}
	
	// starting point
	int s = B;
	for (int j = kMaxLogN - 1; j >= 0; --j) {
		if (A <= L[j][s] && H[L[j][s]] < H[m]) {
			s = L[j][s];
		}
	}
	
	int jumps = 0;
	if (A <= L[0][s]) {
		// next maximum can jump over
		if (R[0][L[0][s]] <= D) {
			return 1;
		}
	}
	else {
		// limit height by a[m]
		for (int j = kMaxLogN - 1; j >= 0; --j) {
			if (H[higher[j][s]] <= H[m]) {
				jumps |= (1 << j);
				s = higher[j][s];
			}
		}
		
		// stopped at m
		if (s == m) {
			return R[0][s]<=D ? jumps+1 : -1;
		}
		
		// if jump over
		if (0 < L[0][s] && R[0][L[0][s]] <= D) {
			return jumps+2;
		}
	}
	
	for (int j = kMaxLogN - 1; j >= 0; --j) {
		if (R[j][s] < C) {
			jumps += (1 << j);
			s = R[j][s];
		}
	}
	
	return C<=R[0][s]&&R[0][s]<=D ? jumps+1 : -1;
}

• Subtask 1: 4 / 4
• Subtask 2: 8 / 8
• Subtask 3: 13 / 13
• Subtask 4: 12 / 12
• Subtask 5: 23 / 23
• Subtask 6: 21 / 21
• Subtask 7: 19 / 19