FrogRiverOne.js

// 2. Frog River One
// Problem:
// A frog wants to jump across a river. The river is divided into positions 1...X. Given an array A where A[K] represents a leaf falling at position A[K], find the earliest time when all positions are covered.

// Example:
// Input: X = 5, A = [1, 3, 1, 4, 2, 3, 5, 4]
// Output: 6

// Solution Idea:

// Use a set to track positions where leaves have fallen.
// If the size of the set equals X, return the index.
// Time Complexity: O(n).


function frogRiverOne(X, A) {
    // Create a set to track positions where leaves fall
    const positions = new Set();

    // Loop through the list of leaves
    for (let i = 0; i < A.length; i++) {
        // Add the current position to the set
        positions.add(A[i]);

        // Check if all positions are covered (i.e., if the size of the set is X)
        if (positions.size === X) {
            // If all positions are covered, return the index (time) when this happens
            return i;
        }
    }

    // If not all positions are covered, return -1
    return -1;
    
}