Upside-down cake

{
  "palindrome": {
    "0": "a",
	"length":"1000",
	"999":"a"  
  }
}

创建一个对象,对象的length是1000
然后给0和999填数据,得到flag

const validatePalindrome = (string) => {
	if (string.length < 1000) {
		return 'too short';
	}

	for (const i of Array(string.length).keys()) {
		const original = string[i];
		const reverse = string[string.length - i - 1];
        
		if (original !== reverse || typeof original !== 'string') {
			return 'not palindrome';
		}
	}

	return null;
}

善于调试

Keys of Array: [ 0 ]
Index: 0, Original: a, Reverse: a, Type of Original: string

const express = require('express');
const bodyParser = require('body-parser');

const app = express();
app.use(bodyParser.json());

const validatePalindrome = (string) => {
    if (string.length < 1000) {
        return 'too short';
    }
    console.log(`String: ${string}, Length: ${string.length}`);
    for (const i of Array(string.length).keys()) {

        const original = string[i];
        const reverse = string[string.length - i - 1];
        const keysArray = [...Array(string.length).keys()];
        console.log(`Keys of Array:`, keysArray);

        console.log(`Index: ${i}, Original: ${original}, Reverse: ${reverse}, Type of Original: ${typeof original}`);
        if (original !== reverse || typeof original !== 'string') {
            return 'not palindrome';
        }
    }

    return 'It is a palindrome!';
}

app.post('/', (req, res) => {
    const result = validatePalindrome(req.body.palindrome);
    res.send(result);
});

app.listen(3000, () => {
    console.log('Server running on http://localhost:3000');
});