LeetCode Js-8. String to Integer (atoi)

    AllenLi
    LeetCode Js-String

    Implement the myAtoi(string s) function, which converts a string to a 32-bit signed integer (similar to C/C++’s atoi function).

    實現 myAtoi(string s)函式，每一個 a 字串的轉換為 32 位元符號整數。

- 忽略字串前方的前導空格。
- 檢查字串前的「-」與「+」符號，並給予正確的渲染。
- 當下一個非數字字串時，將其餘部分忽略。
- 如傳入空值時，則回覆 0。
- 回傳介於 -2^31 <= a <= 2^31。

ex. Atoi = ASCII to integer

    Constraints:

    1.0 <= s.length <= 200
2.s consists of English letters (lower-case and upper-case),
   digits (0-9), ' ', '+', '-', and '.'.

    Note:
    Only the space character ' ' is considered a whitespace character.
    Do not ignore any characters other than the leading whitespace or the rest of the string after the digits.

    Example 1:

    Input: s = "42"
Output: 42

    Example 2:

    Input: s = "   -42"
Output: -42

    Example 3:

    Input: s = "4193 with words"
Output: 4193

    solution:
    1.確認數值的正負狀態
    如果是「+」，則default = 1
    如果是「-」，則default = -1
    2.確認數值是否為整數
    移除前後空白
    3.確認數值後是否有文字
    移除不考慮
    4.數值的處理
    詳請閱FlowChart

    Code 1

    var myAtoi = function(s: string): number {
  // "   -321321 bunnies" 
  //ignore leading whitespaces
  let index: number = 0;
  while (s[index] === " ") {
    index++
  }
  //check if the next character is '-' or '+'
  let sign: number = 1 //default to '+'
  if (s[index] === '+') {
    sign = 1
    index++
  } else if (s[index] === "-") {
    sign = -1
    index++
  }
  //read string of digits into integer
  const digits: Record = {}
  for (let i = 0; i < 10; i++) {
    digits[i + ""] = i
  }
  let result: number = 0
  for (let i = index; i < s.length; i++) {
    if (digits[s[i]] !== undefined) { // is digit
      result = result * 10 + digits[s[i]] //重點
    } else {
      break
    }
  }
  // clamped to max or min
  result = result * sign
  if (result < -1 * Math.pow(2, 31)) {
    result = -1 * Math.pow(2, 31)
  } else if (result > Math.pow(2, 31) - 1) {
    result = Math.pow(2, 31) - 1
  }
  return result
};

    FlowChart:
    Example 1

    result = 0
result = result * 10 + digits[s[i]] => 0 + 4 = 4
result = result * 10 + digits[s[i]] => 4 * 10 + 2 = 42

    Output = 42

    Example 2:

    (s[count] === " ") => count = 1
(s[count] === " ") => count = 2
(s[count] === " ") => count = 3
(s[count] === " ") => count = 4
(s[count]) === "-") => default = -1;count = 5

result = 0
result = result * 10 + digits[s[i]] => 0 + 4 = 4
result = result * 10 + digits[s[i]] => 4 * 10 + 2 = 42

default * result = -1 * 42 => -42

    Output = -42

    Example 3:

    
result = 0
result = result * 10 + digits[s[i]] => 0 + 4 = 4
result = result * 10 + digits[s[i]] => 4 * 10 + 1 = 41
result = result * 10 + digits[s[i]] => 41 * 10 + 9 = 419
result = result * 10 + digits[s[i]] => 419 * 10 + 3 = 4193

(digits[s[i]] === underfined) => break

    Output = 4193

    Success
    Details
    Runtime: 131 ms, faster than 22.67% of JavaScript online submissions for String to Integer (atoi).
    Memory Usage: 45.3 MB, less than 31.49% of JavaScript online submissions for String to Integer (atoi).

    Learning URL

    Code 2

    var myAtoi = function(s: string): number {
    const res: number = parseInt(s) || 0;

    if (res > 2**31 - 1) return 2**31 - 1;
    if (res < 2**31 * - 1) return 2**31 * -1;
    return res;
};

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