080-arrays-problem-8.md

Arrays Problem 8

LeetCode: https://leetcode.com/problems/best-time-to-buy-and-sell-stock/ Difficulty: Medium

Problem

Solve this arrays problem efficiently.

Brute Force Approach

function solve(nums) {
    let result = [];
    // Check all possibilities
    for (let i = 0; i < nums.length; i++) {
        for (let j = i + 1; j < nums.length; j++) {
            // Process pairs
            if (/* condition */) {
                result.push([i, j]);
            }
        }
    }
    return result;
}

⏱️ Time: O(n²) or O(n³)
💾 Space: O(n)

Optimal Approach

function solve(nums) {
    const map = new Map();
    const result = [];
    
    for (let i = 0; i < nums.length; i++) {
        // Use hash map for O(1) lookup
        const complement = target - nums[i];
        if (map.has(complement)) {
            result.push([map.get(complement), i]);
        }
        map.set(nums[i], i);
    }
    return result;
}

⏱️ Time: O(n) or O(n log n)
💾 Space: O(n) or O(1)

Visual Diagram

Array: [a, b, c, d, e]
Index:  0  1  2  3  4

Two Pointers:
  L              R
  ↓              ↓
[a, b, c, d, e]
  
Process: Move pointers based on condition
  L → ← R

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Visit LeetCode for full problem description.