在Javascript数组中查找第一个重复的数字 [英] Find the first repeated number in a Javascript array

问题描述

我需要找到前两个数字并显示如下索引:

I need to find first two numbers and show index like:

var arrWithNumbers = [2,5,5,2,3,5,1,2,4];

因此，第一次重复的编号为 2 ，因此变量 firstIndex 的值应为0.我必须使用for循环.

so the first repeated number is 2 so the variable firstIndex should have value 0. I must use for loop.

var numbers = [7, 5, 7, 6, 6, 4, 9, 10, 2, 11];
var firstIndex

for (i = numbers[0]; i <= numbers.length; i++) {
  firstIndex = numbers[0]
  if (numbers[i] == firstIndex) {
    console.log(firstIndex);
    break;
  }
}

推荐答案

您可以使用

You can use Array#indexOf method with the fromIndex argument.

var numbers = [7, 5, 7, 6, 6, 4, 9, 10, 2, 11];

// iterate upto the element just before the last
for (var i = 0; i < numbers.length - 1; i++) {
  // check the index of next element
  if (numbers.indexOf(numbers[i], i + 1) > -1) {
    // if element present log data and break the loop
    console.log("index:", i, "value: ", numbers[i]);
    break;
  }
}

---

更新:使用对象来引用element的索引会使其更好.

---

UPDATE : Use an object to refer the index of element would make it far better.

var numbers = [7, 5, 7, 6, 6, 4, 9, 10, 2, 11],
  ref = {};

// iterate over the array
for (var i = 0; i < numbers.length; i++) {
  // check value already defined or not
  if (numbers[i] in ref) {
    // if defined then log data and brek loop
    console.log("index:", ref[numbers[i]], "value: ", numbers[i]);
    break;
  }
  // define the reference of the index
  ref[numbers[i]] = i;
}

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