7.reverse-integer.md

整数反转

题目

思路

最简单的方式是直接将数字转为字符串, 然后split成数组, 反转后, 过滤掉-符号, 再转为数字.

/**
 * @param {number} x
 * @return {number}
 */
var reverse = function(x) {
  const MAX = Math.pow(2, 31)
  const inRange = num => (num < MAX) && (num > 1 - MAX)
  if (!inRange(x)) return 0
  const arr = (x + '').split('')
  const isNegative = x < 0
  const noSymbol = str => str !== '-'
  const str = arr.filter(noSymbol).reverse().join('')
  const num = isNegative ? (0 - Number(str)) : (0 + Number(str))
  return inRange(num) ? num : 0
};

以上方法涉及到类型转换, 不转换的时候可以直接对数字进行运算, 通过不断将原数据除10, 相加到另一数字上, 来获得最终的数据.

/**
 * @param {number} x
 * @return {number}
 */
var reverse = function(x) {
  const MAX = 2147483647
  const MIN = -2147483648
  const inRange = num => (num < MAX) && (num > MIN)
  if (!inRange(x)) return 0
  let result = 0
  const isNegative = x < 0
  let source = Math.abs(x)
  let length = 0
  while (++length <= 10) {
    const tmp = source % 10
    source = (source / 10) >>> 0
    result = (tmp < 1 && source < 1) ? result : (result * 10 + tmp)
    console.log(length, tmp, source, result)
  }
  const num = isNegative ? (0 - result) : (0 + result)
  return inRange(num) ? num : 0
};
reverse(1534236469)