确定有限状态自动机

剑指 Offer 20. 表示数值的字符串

image.png

  1. var isNumber = function(s) {
  2.     const states = [
  3.         { space: 0, sign: 1, digit: 2, dot: 4 },
  4.         { digit: 2, dot: 4 },
  5.         { digit: 2, dot: 3, e: 5, space: 8},
  6.         { digit: 3, e: 5, space: 8 },
  7.         { digit: 3 },
  8.         { sign: 6, digit: 7 },
  9.         { digit: 7 },
  10.         { digit: 7, space: 8 },
  11.         { space: 8 }
  12.     ];
  13.     let index = 0;
  14.     for (let i=0; i<s.length; i++) {
  15.         let cur = s.charAt(i);
  16.         if ((/\d/.test(cur))) {
  17.             t = 'digit'
  18.         } else if (['+', '-'].includes(cur)) {
  19.             t = 'sign'
  20.         } else if (['e', 'E'].includes(cur)) {
  21.             t = 'e'
  22.         } else if ('.' == cur) {
  23.             t = 'dot'
  24.         } else if (' ' == cur) {
  25.             t = 'space'
  26.         } else {
  27.             t = 'unknown'
  28.         }
  29.         if (!states[index].hasOwnProperty(t)) return false;
  30.         index = states[index][t]
  31.     }
  32.     return [2,3,7,8].includes(index);
  33. };

数学问题

剑指 Offer 66. 构建乘积数组