txt LeetCode 75 Solutions - Java: 6x9 Edition (English Edition)

Seventy-five problems. Three pages each. One conversation you can actually have.

You do not need two thousand problems. You need seventy-five, and you need to be able to talk about them.

Most people can write the code. Far fewer can say why it is correct while they are writing it, and that is what a ninety-minute screen is actually scoring. This book is built for that gap.

Every problem runs over three pages.

• The answer. Complete, readable Java, with its time and space cost on the same page. No fragments, no "left as an exercise".
• How it works. The idea in plain sentences, a hand-traced run of the case that actually catches people out, and the questions to ask before you write a line.
• In the interview. What is really being tested, the edge cases to name first, the follow-up that is coming next, and a Say this out loud script you can borrow word for word.

Written in Java, not translated into it. Every answer is a standalone method that keeps LeetCode's own method name, so it drops into class Solution unchanged and runs. Java 17 and later, standard library only, nothing to download. Where Java changes the problem, the book says so: why a StringBuilder is not optional, why lo + hi can overflow an int and lo + (hi - lo) / 2 cannot, why an int[] row will not behave as a hash key.

All 75, grouped into the 22 patterns they come from — arrays and strings, two pointers, sliding window, prefix sums, hashing, stacks and queues, linked lists, trees by depth and by breadth, binary search trees, graphs, heaps, binary search, backtracking, dynamic programming in one and two dimensions, bit manipulation, tries, intervals, and monotonic stacks. Recognise the pattern and you have recognised a family, not a puzzle.

Built to be worked, not read. Read the problem, cover the rest of the spread, write your own solution, then compare. What you learn is in the difference. Every problem carries a QR code straight to it, so the book sits open next to the editor instead of competing with it.

Printed clean in black and white for the page, so it stays readable under bad light, on a train, and the night before.

Nobody walks into an interview knowing every problem. What you walk in with is a small set of patterns, recognised on sight, and the habit of thinking out loud while your hands stay steady.