添加到数组中的额外元素

Question

我试图以新手的身份解决这个问题，并且在循环后我在返回的数组中看到了额外的元素。

In DNA strings, symbols "A" and "T" are complements of each other, as "C" and "G". 
You have function with one side of the DNA, you need to get the other complementary side.

这是我的解决方案

let dnaComStrand = [];
const DNAStrand = function (dnaStrand) {
  for (let i = 0; i < dnaStrand.length; i++) {
    if (dnaStrand[i] === `A`) {
      dnaComStrand[i] = `T`;
    } else if (dnaStrand[i] === `T`) {
      dnaComStrand[i] = `A`;
    } else if (dnaStrand[i] === `C`) {
      dnaComStrand[i] = `G`;
    } else if (dnaStrand[i] === `G`) {
      dnaComStrand[i] = `C`;
    }
  }
  //   return dnaComStrand.join(``);
  return dnaComStrand;
};
console.log(DNAStrand(`GCATA`));

然而在我看到的控制台中

Array(5) [ "C", "G", "T", "A", "T" ]

如果我再次尝试调用该函数，这会变得更加混乱。

console.log(DNAStrand([`T`, `C`, `G`]));

导致

Array(5) [ "A", "G", "C", "A", "T" ]

这些额外的元素是从哪里来的？？ 提前致谢

Answer 1

你可以做：

 const hash = { A: 'T', T: 'A', C: 'G', G: 'C', } const DNAStrand = dnaStrand => dnaStrand.split('').map(c => hash[c]) // 1 const dnaComStrand1 = DNAStrand(`GCATA`) console.log(dnaComStrand1) // 2 const dnaComStrand2 = DNAStrand(dnaComStrand1.join('')) console.log(dnaComStrand2)

Answer 2

使用函数内部和循环之前的一组新元素重新初始化数组。