1
const toNumber = (s) => {
2
  let res = 0;
3
  for (let i = 0; i < s.length; i++) {
4
    res = res * 10 + (s.charCodeAt(i) - "0".charCodeAt(0));
5
  }
6

7
  return res;
8
};
9

10
var myAtoi = function (s) {
11
  s = s.trim();
12
  let r = s.match(/^(\d+|[+-]\d+)/);
13

14
  if (r) {
15
    let m = r[0],
16
      res;
17
    switch (m[0]) {
18
      case "-":
19
        res = toNumber(m.slice(1)) * -1;
20
        break;
21
      case "+":
22
        res = toNumber(m.slice(1));
23
        break;
24
      default:
25
        res = toNumber(m);
26
        break;
27
    }
28

29
    if (res < 1 << 31) return 1 << 31;
30
    if (res > -(1 << 31) - 1) return -(1 << 31) - 1;
31
    return res;
32
  }
33

34
  return 0;
35
};