ip算法

function ip(str) {
  var length = str.length;
  var ans = [];
  var stack = [];
  var step = 0;
  var lastStep = 0;
  var lastchar = ''

  // 生成原始数组
  for (var i = 0; i < 32; i++) {
    ans[i] = 0;
  }

  // 处理每一次相加
  function handle() {
    if (stack.length === 0) {
      if (lastchar === 'b') {
        ans[step] = 1;
      } else {
        ans[step] = 0;
      }
      step++;
    } else {
      var nStep = 0;
      stack.forEach(function(item, index) {
        if (index === 0) {
          nStep += item;
        } 
        if (index === 1) {
          nStep += (10 * item)
        }
      });
      if (lastchar === 'b') {
        for (var i = step; i < step + nStep; i++) {
          ans[i] = 1;
        }
      } else {
        for (var i = step; i < step + nStep; i++) {
          ans[i] = 0;
        }
      }
      step += nStep;
    }
  }

  for (var i = length - 1; i >= 0; i--) {
    // 每次处理一次变更
    if ((str[i] === 'a' || str[i] === 'b') && i != (length - 1)) {
      handle();
      stack = [];
    } 
    if (str[i] === 'a' || str[i] === 'b') {
      lastchar = str[i];
    } else {
      stack.push(Number(str[i]));
    }
  }
  handle();
  console.log(ans.join(''));
  var ips = [];

  // 把数组转换城字符输出
  for (var i = 0; i < 4; i++) {
    var temp = 0
    for (var j = 0; j < 8; j++) {
      if (ans[i * 8 + j] === 1) {
        temp += Math.pow(2, j);
      }
    }
    ips[i] = temp;
  }
  return ips[3] + '.' + ips[2] + '.' + ips[1] + '.' + ips[0];
}

var ans = ip('7ab7ab7a2b6ab');
console.log(ans);
console.log(ans === '1.1.1.129');

var ans = ip('32a');
console.log(ans);

var ans = ip('32b');
console.log(ans);

var ans = ip('8b8a8b8a');
console.log(ans);

var ans = ip('a7b8a8a7ab');
console.log(ans);
var ans = ip('aa6baa6baa6b8a');
console.log(ans);