Irene | Global Tech x GenAI on Instagram: "Prefix Sum took me a LOT longer than Two Pointers — so if you’re struggling with it too, here’s what finally helped me: 1️⃣ Don’t try to learn everything at once. Prefix sum isn’t just “sum of subarrays.” It has sub-patterns — hash maps, modulo, XOR, 2D grids, difference arrays. Break it down. Learn one variation per day. 2️⃣ Build the prefix by hand. Literally write the array, the prefix array, and the equation pref[r+1] - pref[l]. If you can visualize

Govind Pothuraju on Instagram: "Day 39/200: The Power of Prefix Sum — The Trick Every Top Coder Knows! ⚡ Have you ever calculated the sum of elements in a subarray using two loops? That’s slow ❌ — let’s make it lightning fast ⚡ ✅ Prefix Sum Formula: prefix[i] = prefix[i-1] + arr[i] ✅ Query Example: To get sum from index l to r: prefix[r] - prefix[l-1] Example: Input: arr = [2, 3, 5, 1, 6] Prefix: [2, 5, 10, 11, 17] Sum(1,3) = prefix[3] - prefix[0] = 11 - 2 = 9 💡 Why it’s powerful: Speeds