A sequence x1, x2, ..., xn is Fibonacci-like if: n >= 3 xi + xi+1 == xi+2 for all i + 2 <= n Given a strictly increasing array arr of positive integers forming a sequence, return the length of the longest Fibonacci-like subsequence of arr. If one do

lenLongestFibSubseq.js

/**
 * @param {number[]} arr
 * @return {number}
 */
var lenLongestFibSubseq = function(arr) {
    const n = arr.length;
    if (n < 3) return 0;

    const indexMap = new Map();
    for (let i = 0; i < n; i++) {
        indexMap.set(arr[i], i);
    }

    const dp = new Map();
    let maxLength = 0;

    // Iterate over all pairs (i, j) where i < j.
    for (let j = 0; j < n; j++) {
        for (let i = 0; i < j; i++) {
            const x = arr[i];
            const y = arr[j];
            const z = x + y;

            // Check if z is in the array.
            if (indexMap.has(z)) {
                const k = indexMap.get(z);
                const key = `${y},${z}`; // Create a unique key for the pair (y, z).
                const prevKey = `${x},${y}`; // Create a unique key for the pair (x, y).

                const newLength = (dp.get(prevKey) || 2) + 1;
                dp.set(key, newLength);
                maxLength = Math.max(maxLength, newLength);
            }
        }
    }

    return maxLength >= 3 ? maxLength : 0;
};