典型061 スタック2本

typical90_061.js

function *main() {
  const Q = +(yield);
  const head = [], tail = [];
  for (let i = 0; i < Q; i++) {
    const [t, x] = (yield).split(" ").map(Number);
    if (t == 1) {
      head.push(x);
    } else if (t == 2) {
      tail.push(x);
    } else if (t == 3) {
      if (x <= head.length) {
        console.log(head[head.length - x]);
      } else {
        console.log(tail[x - head.length - 1]);
      }
    }
  }
}

const iter = main();
iter.next();
require("readline").createInterface({input: process.stdin}).on("line", line => iter.next(line));