Submission #1171060

#	Time	Username	Problem	Language	Result	Execution time	Memory
1171060		baldwin_huang	Rainforest Jumps (APIO21_jumps)	C++20	0 / 100	4032 ms	47428 KiB

jumps

#include <bits/stdc++.h>

using namespace std;

int n;
vector<int> h;
const int INF = 1e9;

struct node {
	int left = -1;
	int right = -1;
};

vector<node> nodes;
vector< vector<int> > binary_lifting(262144 + 1, vector<int>(32, -1)); // It tells you the 2^j ancestor of i.

void init(int N, vector<int> H) {
	n = N;
	h = H;
	nodes = vector<node>(n); // It's a graph, has the index to the children.

	for (int i = 1; i < n; i++) {
		int target = i - 1;
		while (H[target] <= H[i]) {
			if (target == -1) {
				break;
			}
			target = nodes[target].left;
		}
		nodes[i].left = target;
	}

	for (int i = n - 2; i >= 0; i--) {
		int target = i + 1;
		while (H[target] <= H[i]) {
			if (target == -1) {
				break;
			}
			target = nodes[target].right;
		}
		nodes[i].right = target;
	}

	// Create the binary_lift

	// Create the base ancestors;
	for (int i = 0; i < n; i++) {
		int greatest = -1;
		int ancestor = -1;
		if (nodes[i].left != -1 && greatest < H[nodes[i].left]) {
			greatest = H[nodes[i].left];
			ancestor = nodes[i].left;
		}
		if (nodes[i].right != -1 && greatest < H[nodes[i].right]) {
			greatest = H[nodes[i].right];
			ancestor = nodes[i].right;
		}
		binary_lifting[i][0] = ancestor;
	}

	for (int i = 1; i < 32; i++) {
		for (int j = 0; j < n; j++) {
			if (binary_lifting[j][i - 1] == -1) {
				binary_lifting[j][i] = -1;
			}
			else {
				binary_lifting[j][i] = binary_lifting[binary_lifting[j][i - 1]][i - 1];
			}
		}
	}

	return;
}

int next_jump(int a, int c) {
	if (a == -1) {
		return -1;
	}
	int greatest = -1;
	int ancestor = -1;
	if (nodes[a].left != -1 && greatest < h[nodes[a].left] && h[nodes[a].left] <= h[c]) {
		greatest = h[nodes[a].left];
		ancestor = nodes[a].left;
	}
	if (nodes[a].right != -1 && greatest < h[nodes[a].right] && h[nodes[a].right] <= h[c]) {
		greatest = h[nodes[a].right];
		ancestor = nodes[a].right;
	}
	return ancestor;
}

// Gives the index to the jth ancestor
int find_ancestor(int source, int distance) {
	int pos = source;
	for (int i = 31; i >= 0; i--) {
		if (distance & (1<<i)) {
			pos = binary_lifting[pos][i];
			if (pos == -1) {
				return -1;
			}
		}
 	}
	return pos;
}

int minimum_jumps(int A, int B, int C, int D) {

	if (A != B || C != D) {
		return -1;
	}

	int sum = 0;
	bool found = false;
	int X = A;

	while (true) {
		int high = 262144;
		int low = 0;
		int ans = -1;
		while (low <= high) {
			int mid = (low + high) / 2;
			int dist = mid;
			int ancestor1 = find_ancestor(X, dist);
			int ancestor2 = find_ancestor(X, dist + 1);
			// cout << low << ' ' << high << '\n';

			// Check if we have the right answer
			if (ancestor1 != -1 && ancestor2 != -1 && h[ancestor1] < h[C] && h[C] <= h[ancestor2]) {
				ans = dist;
				break;
			}

			// Anything that is greater or equal to C is not wanted.
			if (ancestor1 == -1 || h[C] <= h[ancestor1]) {
				high = mid - 1;
			}
			else {
				low = mid + 1;
			}
		}

		if (ans == -1) {
			// There is nothing more to explore.
			break;
		}
		else {
			sum += ans;
			int next = next_jump(find_ancestor(X, ans), C);
			if (next == -1) {
				break;
			}
			else if (next == C) {
				found = true;
				sum++;
				break;
			}
			else {
				sum++;
				X = next;
			}
		}
	}

	if (found) {
		return sum;
	}
	else {
		return -1;
	}
	
}

• Subtask 1: 0 / 4
• Subtask 2: 0 / 8
• Subtask 3: 0 / 13
• Subtask 4: 0 / 12
• Subtask 5: 0 / 23
• Subtask 6: 0 / 21
• Subtask 7: 0 / 19