在数组中查找重复值时遇到问题

Question

我最近开始了一门课程，我对 JavaScript 很陌生。我正在执行一项任务，该任务需要我找到我的设备达到两次的第一个频率。我得到了 989 个数字，从正数和负数不等，我必须首先找出哪个数字显示为倍频。例如：+3、+3、+4、-2、-4 先达到 10 两次。

我尝试了不同的代码变体，但没有一个给我输出，就好像它因为大量的数字而中断。我需要输入的所有数字的 pastebin 可以在这里找到：https://pastebin.com/VESwwM2y 使用这些数字我必须找到哪个数字首先出现，两次。这是我一直在使用的代码：

function find_duplicate_in_array(arra1) {
    var object = {};
    var result = [];

    arra1.forEach(function (item) {
      if(!object[item])
          object[item] = 0;
        object[item] += 1;
    })

    for (var prop in object) {
       if(object[prop] >= 2) {
           result.push(prop);
       }
    }

    return result;

}

console.log(find_duplicate_in_array([]));

我只需要弄清楚如何让它工作。

Answer 1

您可以使用Array#some 并在找到第一个重复项后停止循环执行

var array = [+4, +3, -15, -8, +15, -17, -16, +15, -10, +1, +17, +19, -10, +17, +11, +3, -13];

function getFirstDuplicate(arr) {
  var obj = {}, duplicate;
  arr.some(function(item) {

    if (!obj[item]) {
      obj[item] = 1;
      return false;
    } else {
      duplicate = item;
      return true;
    }
  });
  return duplicate;
}

console.log(getFirstDuplicate(array))

Answer 2

这应该给你工具

let arr = []; 
let res = [];

const searchIt = (num,i) => { 
  const n=arr.indexOf(num); 
  if (n!==-1) { 
    if (res.indexOf(num) ==-1) res.push(num);
    console.log(num,"@pos",i," found at ",n); 
  }
  arr.push(num);
}

`+4
+3
-15
-8
+15
-17
-16
+15
-10
+1
+17
+19
-10
+17
+11
+3
-13
-13
-20
+10
-7
+2
-12
+2
+2
+7
+7
+19
-18
-10
+16
+18
-9
+15
-16
+15
+15
+14
+13
+15
+2
+6
+10
+12
+13
+8
+3
-19
-12
+19
+13
+4
+16
+16
-10
+15
-16
+17
+16
+5
+1
+17
+15
-16
+3
+17
-9
-4
-11
+2
+19
-12
+9
+8
+8
-7
+17
-15
-17
+18
+9
-11
+10
+5
-18
+15
+12
-3
-2
+18
-1
+5
+12
+3
-7
+16
+3
+4
+17
-13
+7
-13
+3
+7
+13
+4
-10
-13
+4
+13
+15
+14
-13
+10
-9
-16
+4
+18
-13
-11
+13
+8
-11
+18
+19
-16
-6
-5
+16
-10
-14
+7
+10
+10
-16
-19
+10
-5
+13
+24
-1
+9
+2
+12
+11
-4
-17
+2
-17
+8
+18
-10
+2
-6
-2
-12
+21
+16
-21
-7
-6
-7
-3
+14
+16
+3
+10
-14
+2
+15
+9
+13
+4
+2
-9
-9
+4
-2
-11
-9
+16
+9
-6
-17
+22
+8
+16
+5
+9
+18
-5
-1
+13
-8
-11
+10
+6
+9
-1
+13
+11
-3
-12
+17
-19
-11
+10
+17
+15
+9
+9
+4
-3
+9
-4
+8
-7
+12
+5
-2
-6
-17
+12
+18
+14
-1
+15
+12
-19
-16
-4
-4
+1
-9
+5
-6
+4
+16
-1
+18
+5
+17
-1
+5
+15
+4
+3
-11
+5
+18
-3
+2
+7
-13
+10
+21
-7
+6
-2
-20
-11
-12
-18
-7
-15
+9
-1
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-10
-5
-15
+3
-20
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-18
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-6
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-16
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-8
-21
-8
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-15
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-22
+5
+5
-20
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+22
-1
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-17
-14
-15
+2
-8
+11
-4
-37
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-10
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-1
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-5
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-10
+3
-27
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-23
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-27
-41
-5
-41
+144
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+155
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-26
+16
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-229
-70
+401
+64265
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-14
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-2
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-5
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-2
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+16
-6
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-20
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+8
-9
-9
+28
-4
-3
-17
-9
-11
-1
+15
+13
+12
-30
-16
+19
-22
+2
-18
+7
-8
-24
+31
+5
+36
+3
+48
+10
+19
-7
-11
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+3
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+4
-15
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-7
+14
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-3
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-17
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-15
-10
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-4
-17
-13
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-3
-9
+5
+10
-12
-1
+15
+20
-3
-1
-1
-6
+15
-2
+13
+19
-1
+8
+17
+4
+1
+18
+1
+4
+12
+3
-5
-21
-15
-14
+20
+5
+18
-6
-5
-5
+4
-10
+18
-5
+23
+22
+13
-5
+15
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-14
-15
+7
-11
-8
-2
-6
-9
-15
-3
+12
+25
-9
-15
-16
+20
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+25
-6
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+7
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-16
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-9
-21
+13
+14
+6
-16
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-27
-21
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+26
+13
+5
-23
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+9
+20
+14
-32
+27
-2
-16
+21
-92
-12
-14
-25
+4
-21
-9
-14
-14
-6
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+5
+2
-1
-3
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-4
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-10
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-19
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-11
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+8
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-4
-4
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-17
-13
-23
-9
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-20
-17
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-18
-19
-64
+9
-24
-16
-10
+196
+16
-5
+21
-7
+28
+5
+5
-19
+38
-33
+25
+209
+391
-559
+64522
-2
-19
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+17
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-6
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-2
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-11
-17
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-19
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+14
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-16
-6
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+24
-37
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-15
-4
+3
-21
-17
-19
-16
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+9
-13
-20
-30
-7
+10
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-3
+20
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-1
+9
-22
-19
-3
-8
+3
-18
+8
+3
-7
-2
-7
+6
+15
-19
+13
-26
+7
-18
-13
+21
-9
+10
-130255`.split(/\n/).forEach((num,i) => searchIt(num,i))
console.log(res);