COMPILED CANVAS
DSA IN JAVA

Your logic is right. Java still fails your code.

3 traps that fail interviews

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TRAP 1

== on Integer

✗ a == b // false
✓ a.equals(b) // true

Two Integer 1000s are different objects. Use a.equals(b).

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TRAP 2

int overflow

2,147,483,647 + 1 = −2,147,483,648

int stops at about 2.1 billion, then turns negative. Use long for big sums.

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TRAP 3

String + in a loop

StringBuilder sb = new StringBuilder(); for (char c : s.toCharArray()) sb.append(c);

Each + makes a new string. Use StringBuilder.

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TOOLBOX

The 4 you need

ListMapSetDeque

ArrayList, HashMap, HashSet and ArrayDeque cover most DSA problems.

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⚠ MOST PEOPLE MISS THIS

The mistake

Comparing Integer objects with ==. It works for small numbers, then silently breaks.

QUICK QUIZ

Can you get it?

Tap an answer. The full video explains why.

📸 SCREENSHOT THIS

Cheat sheet

  • Compare objects with .equals()
  • Big sums → long
  • Build strings with StringBuilder
  • HashMap: O(1) lookup
  • ArrayDeque for stacks and queues
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