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