ReactJS Program to Memoize Expensive Computation with Explanation
ReactJS
Medium
Performance & Patterns
30 views
1 min read
84 words
This problem helps you practice core ReactJS fundamentals in a practical way. It builds intuition around expensive, render, react. Let’s break it down step by step so you can implement it confidently.
Problem Statement
Calculate heavy derived data once per input change using useMemo.
Input Format
No input.
Output Format
Render a React component.
Constraints
Avoid expensive work on every render.
Code Solution
This explanation is written for learning purposes and to help beginners understand the concept clearly.
import React, { useMemo, useState } from 'react';
function heavyScore(text) {
let score = 0;
for (let i = 0; i < 80000; i++) {
const c = text.charCodeAt(i % (text.length || 1));
score = (score + c * 17 + i) % 100000;
}
return score;
}
export default function App() {
const [text, setText] = useState('meetcode');
const score = useMemo(() => heavyScore(text), [text]);
return (
<div style={{ padding: 16, width: 520 }}>
<h2 style={{ marginTop: 0 }}>Derived score</h2>
<input value={text} onChange={(e) => setText(e.target.value)} style={{ width: '100%', padding: '10px 12px', borderRadius: 12, border: '1px solid #bbb' }} />
<div style={{ marginTop: 10, color: '#555' }}>Score: {score}</div>
</div>
);
}
Output Example
No sample I/O is provided for this question.
Common Mistakes
- Misreading input/output format.
- Not handling constraints and edge cases.
- Off-by-one errors in loops.
- Forgetting to reset variables between test cases (if any).
Solution Guide
Problem
Calculate heavy derived data once per input change using useMemo.
Input / Output
Output
Render a React component.
Constraints
Avoid expensive work on every render.
Details
Common Mistakes
- Misreading input/output format.
- Not handling constraints and edge cases.
- Off-by-one errors in loops.
- Forgetting to reset variables between test cases (if any).
Difficulty
Medium
ReactJS
Official Solution
import React, { useMemo, useState } from 'react';
function heavyScore(text) {
let score = 0;
for (let i = 0; i < 80000; i++) {
const c = text.charCodeAt(i % (text.length || 1));
score = (score + c * 17 + i) % 100000;
}
return score;
}
export default function App() {
const [text, setText] = useState('meetcode');
const score = useMemo(() => heavyScore(text), [text]);
return (
<div style={{ padding: 16, width: 520 }}>
<h2 style={{ marginTop: 0 }}>Derived score</h2>
<input value={text} onChange={(e) => setText(e.target.value)} style={{ width: '100%', padding: '10px 12px', borderRadius: 12, border: '1px solid #bbb' }} />
<div style={{ marginTop: 10, color: '#555' }}>Score: {score}</div>
</div>
);
}
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