8. String to Integer (atoi)

Implement atoi: skip leading spaces, read an optional sign, then read digits until a non-digit. Clamp the result to the signed 32-bit range; return 0 if no digits were read.

Skip spaces, read a sign, then fold digits into the result. Before each multiply-by-10, check whether it would overflow and clamp right away.

1function myAtoi(s: string): number {
2  let i = 0, sign = 1, res = 0;
3  while (s[i] === " ") i++;
4  if (s[i] === "+" || s[i] === "-") sign = s[i++] === "-" ? -1 : 1;
5  while (i < s.length && s[i] >= "0" && s[i] <= "9") {
6    const d = +s[i++];
7    if (res > (2 ** 31 - 1 - d) / 10) return sign === 1 ? 2 ** 31 - 1 : -(2 ** 31);
8    res = res * 10 + d;
9  }
10  return sign * res || 0;
11}

sign = 1res = 0

s

Skip a leading space.

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