Exact Change

设计一个收银程序 checkCashRegister() ，其把购买价格(price)作为第一个参数 , 付款金额 (cash)作为第二个参数, 和收银机中零钱 (cid) 作为第三个参数.

cid 是一个二维数组，存着当前可用的找零.

当收银机中的钱不够找零时返回字符串 "Insufficient Funds". 如果正好则返回字符串 "Closed".

否则, 返回应找回的零钱列表,且由大到小存在二维数组中.

题目解读： 使用cid项 能否的组合出cash - price 值，可以则返回"Closed", 小于则返回"Insufficient Funds"，否则返回由大到小零钱列表的二维数组.

var drawer = {
  PENNY: 0.01,
  NICKEL: 0.05,
  DIME: 0.10,
  QUARTER: 0.25,
  ONE: 1,
  FIVE: 5,
  TEN: 10,
  TWENTY: 20,
  'ONE HUNDRED': 100
};

function checkCashRegister(price, cash, cid) {
  var change = cash - price;
  var total = 0;

  //计算零钱总额
  for (var i = 0; i < cid.length; i++) {
    total += cid[i][1];
  }
  total = Number(total.toFixed(2));

  if (total < change) {
    return "Insufficient Funds";
  } else if (total === change) {
    return "Closed";
  } else {
    return payBack(change, cid, total);
  }
}

function payBack(change, cid, total) {
  var back = [];
  for (var i = cid.length - 1; i >= 0; i--) {
    var type = cid[i][0];
    var money = cid[i][1];
    if (money === 0) continue;

    if (money < change) {
      back.push(cid[i]);
      change -= money;
    } else if (money > change) {
      var drawerCash = Math.floor(change / drawer[type]) * drawer[type];

      if (drawerCash === 0 && total - money < change) {
        return "Insufficient Funds";
      } else if (drawerCash === 0) {
        continue;
      } else {
        var drawerBack = [];
        drawerBack.push(type);
        drawerBack.push(drawerCash);
        back.push(drawerBack);
        change -= drawerCash;
      }
    }
    change = Number(change.toFixed(2));
  }

  if (change === 0) {
    return back;
  } else {
    return "Insufficient Funds";
  }
}