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LeetCode 2940: Find Building Where Alice and Bob Can Meet Solution

Master LeetCode problem 2940 (Find Building Where Alice and Bob Can Meet), a hard challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

Problem Explanation

Explanation:

  • We can solve this problem using a monotonic decreasing stack approach.
  • We will iterate over the buildings from left to right, keeping track of the buildings that Alice and Bob can reach.
  • For each building, we will update the stack to remove any buildings that are not reachable from the current building.
  • If Alice and Bob can reach the same building, we update the answer for the query with the leftmost building index.
  • If Alice and Bob cannot reach a common building, we set the answer to -1.

Solution Code

import java.util.*;

class Solution {
    public int[] findBuildings(int[] heights, int[][] queries) {
        int n = heights.length;
        Stack<Integer> stack = new Stack<>();
        int[] ans = new int[queries.length];
        
        for (int i = 0; i < n; i++) {
            while (!stack.isEmpty() && heights[i] >= heights[stack.peek()]) {
                stack.pop();
            }
            
            stack.push(i);
        }
        
        for (int i = 0; i < queries.length; i++) {
            int ai = queries[i][0];
            int bi = queries[i][1];
            boolean found = false;
            
            while (!stack.isEmpty() && stack.peek() <= ai) {
                stack.pop();
            }
            
            if (!stack.isEmpty() && stack.peek() < bi) {
                ans[i] = stack.peek();
                found = true;
            }
            
            if (!found) {
                ans[i] = -1;
            }
        }
        
        return ans;
    }
}

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