js double bitwise not ~~ All In One

js double bitwise not ~~ All In One

js 双非位运算 ~~

0 vs NaN

const arr = [];
// []
~~arr.pop();
// 0
+arr.pop();
// NaN

const arr = [];
// []
const a = arr.pop();
// undefined
~~a;
// 0
+a;
// NaN

demos

const addStrings = function(str1, str2) {
  let res = '';
  let temp = 0;
  const arr1 = str1.split('');
  const arr2 = str2.split('');
  while (arr1.length || arr2.length || temp) {
    // string => number ✅
    let a = ~~arr1.pop();
    let b = ~~arr2.pop();
    console.log(`a, b`, a, b);
    temp += a + b;
    console.log(`temp`, temp);
    // 字符串相加，要注意先后顺序
    res = (temp % 10) + res;
    // 进位
    temp = temp > 9 ? 1 : 0;
  }
  // 正则表达式去除头部的 0
  return res === "0" ? res : res.replace(/^0+/, '');
}

/*
addStrings([1,0,0,0,0,1].join(``), [4, 5, 6].join(``));
a, b 1 6
temp 7
a, b 0 5
temp 5
a, b 0 4
temp 4
a, b 0 0
temp 0
a, b 0 0
temp 0
a, b 1 0
temp 1
'100457'
*/

const addStrings = function(str1, str2) {
  let res = '';
  let temp = 0;
  const arr1 = str1.split('');
  const arr2 = str2.split('');
  while (arr1.length || arr2.length || temp) {
    // string => number ❌  NaN bug
    let a = +arr1.pop();
    let b = +arr2.pop();
    console.log(`a, b`, a, b);
    temp += a + b;
    console.log(`temp`, temp);
    // 字符串相加，要注意先后顺序
    res = (temp % 10) + res;
    // 进位
    temp = temp > 9 ? 1 : 0;
  }
  // 正则表达式去除头部的 0
  return res === "0" ? res : res.replace(/^0+/, '');
}

addStrings([1,0,0,0,0,1].join(``), [4, 5, 6].join(``));

/*
a, b 1 6
temp 7
a, b 0 5
temp 5
a, b 0 4
temp 4
a, b 0 NaN
temp NaN
a, b 0 NaN
temp NaN
a, b 1 NaN
temp NaN
'NaNNaNNaN457'

*/

bugs

❌ NaN bug +undefined => NaN

const addStrings = function(str1, str2) {
  let res = '';
  let temp = 0;
  const arr1 = str1.split('');
  const arr2 = str2.split('');
  while (arr1.length || arr2.length || temp) {
    // string => number ❌  NaN bug
    temp += +arr1.pop() + +arr2.pop();
    console.log(`temp`, temp);
    // 字符串相加，要注意先后顺序
    res = (temp % 10) + res;
    // 进位
    temp = temp > 9 ? 1 : 0;
  }
  // 正则表达式去除头部的 0
  return res === "0" ? res : res.replace(/^0+/, '');
}

addStrings([1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1].join(``), [4, 5, 6].join(``));

/*
temp 7
temp 5
temp 4
28 x temp NaN
'NaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaN457'
*/

solutions

✅ ~~undefined => 0

const addStrings = function(str1, str2) {
  let res = '';
  let temp = 0;
  const arr1 = str1.split('');
  const arr2 = str2.split('');
  while (arr1.length || arr2.length || temp) {
    // string => number ✅
    // ~~ double bitwise not / 双非位运算
    temp += ~~arr1.pop() + ~~arr2.pop();
    console.log(`temp`, temp);
    // 字符串相加，要注意先后顺序
    res = (temp % 10) + res;
    // 进位
    temp = temp > 9 ? 1 : 0;
  }
  // 正则表达式去除头部的 0
  return res === "0" ? res : res.replace(/^0+/, '');
}

addStrings([1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1].join(``), [4, 5, 6].join(``));

/*
2 x temp 6
temp 4
27 x temp 0
 temp 1
'1000000000000000000000000000466'
*/

避免 +undefined => NaN ✅

// 字符串相加 / 大数相加
const addStrings = function(str1, str2) {
  let res = '';
  let temp = 0;
  const arr1 = str1.split('');
  const arr2 = str2.split('');
  while (arr1.length || arr2.length || temp) {
    // ~~ double bitwise not / 双非位运算 ✅
    // temp += ~~arr1.pop() + ~~arr2.pop();
    // string => number ✅
    if(arr1.length && arr2.length) {
      let a = +arr1.pop()
      let b = +arr2.pop();
      temp += a + b;
    } else {
      if(arr1.length) {
        let a = +arr1.pop()
        temp += a;
      }
      if(arr2.length) {
        let b = +arr2.pop();
        temp += b;
      }
    }
    // string => number ❌
    // temp += +arr1.pop() + +arr2.pop();
    // 字符串相加，要注意先后顺序
    res = (temp % 10) + res;
    // 进位
    temp = temp > 9 ? 1 : 0;
  }
  // console.log('res =', res, typeof res);
  return res === "0" ? res : res.replace(/^0+/, '');
}

js 大数相加，科学计数法 bug

const a = parseInt([1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1].join(``));
const b = parseInt([4, 6, 5].join(``));
const sum = a + b;
// 1e+30 ❌

//  wanted ✅
// 1000000000000000000000000000466

BigInt

digits = [6,1,4,5,3,9,0,1,9,5,1,8,6,7,0,5,5,4,3]
// (19) [6, 1, 4, 5, 3, 9, 0, 1, 9, 5, 1, 8, 6, 7, 0, 5, 5, 4, 3]
BigInt(digits.join(''))
// 6145390195186705543n

BigInt(digits.join('')).toString().split("").map(Number)
// (19) [6, 1, 4, 5, 3, 9, 0, 1, 9, 5, 1, 8, 6, 7, 0, 5, 5, 4, 3]

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt

Number.MAX_SAFE_INTEGER

The Number.MAX_SAFE_INTEGER static data property represents the maximum safe integer in JavaScript (2**53 – 1).

Number.MAX_SAFE_INTEGER 静态数据属性表示 JavaScript 中的最大安全整数 (2**53 – 1)。

Number.MAX_SAFE_INTEGER
9007199254740991
2 ** 64 - 1
18446744073709552000
2 ** 32 - 1
4294967295

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/MAX_SAFE_INTEGER

refs

https://www.cnblogs.com/xgqfrms/p/18230786

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