Submission #1170574

#	Time	Username	Problem	Language	Result	Execution time	Memory
1170574		baldwin_huang	Rainforest Jumps (APIO21_jumps)	C++20	0 / 100	122 ms	42520 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>(30, -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 < 30; 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;
}

// Gives the index to the jth ancestor
int find_ancestor(int source, int distance) {
	int pos = source;
	for (int i = 29; 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 high = 200010;
	int low = 0;
	int ans;
	while (low <= high) {
		int mid = (low + high) / 2;
		int dist = mid;
		int ancestor = find_ancestor(A, dist);
		// cout << low << ' ' << high << '\n';
		// Anything that is greater or equal to C is not wanted.
		if (ancestor == -1 || h[C] <= h[ancestor]) {
			high = mid - 1;
		}
		else {
			ans = dist;
			low = mid + 1;
		}
	}

	int ancestor = find_ancestor(A, ans);
	// cout << find_ancestor(A, 4) << '\n';

	if (h[nodes[ancestor].left] == h[C] || h[nodes[ancestor].right] == h[C]) {
		return ans + 1;
	}
	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