牛客 101

const rl = require("readline").createInterface({ input: process.stdin });
var iter = rl[Symbol.asyncIterator]();
const readline = async () => (await iter.next()).value;

void (async function () {
    let line;
    while ((line = await readline())) {
        let count = parseInt(line);
        if (isNaN(count)) break;

        let arrStr = await readline();
        let arr = Array.from(arrStr.split(" ").map(Number));

        let res = 0;
        let firstPos = new Map(); // 哈希表：记录每个数字第一次出现的下标

        for (let i = 0; i < arr.length; i++) {
            let num = arr[i];
            if (firstPos.has(num)) {
                // 如果这个数字之前出现过，计算距离
                // 题目要求的距离是中间隔了多少个元素，所以是 j - i - 1
                let distance = i - firstPos.get(num) - 1;
                res = Math.max(res, distance);
            } else {
                // 如果是第一次遇到这个数字，记录下它的下标
                firstPos.set(num, i);
            }
        }
        console.log(res);
    }
})();