問題描述

可能重復:
在 javascript 數組中查找重復值的最簡單方法

如何檢查數組是否有重復值?

How do I check if an array has duplicate values?

如果數組中的某些元素相同，則返回true.否則，返回 false.

If some elements in the array are the same, then return true. Otherwise, return false.

['hello','goodbye','hey'] //return false because no duplicates exist
['hello','goodbye','hello'] // return true because duplicates exist

請注意，我不關心查找重復項，只需要布爾結果數組是否包含重復項.

Notice I don't care about finding the duplication, only want Boolean result whether arrays contains duplications.

推薦答案

如果你有一個 ES2015 環境(在寫這篇文章時:io.js, IE11, Chrome, Firefox, WebKit nightly)，那么下面的將起作用，并且會很快(即 O(n)):

If you have an ES2015 environment (as of this writing: io.js, IE11, Chrome, Firefox, WebKit nightly), then the following will work, and will be fast (viz. O(n)):

function hasDuplicates(array) {
    return (new Set(array)).size !== array.length;
}

<小時>

如果您只需要數組中的字符串值，則可以使用以下方法:

If you only need string values in the array, the following will work:

function hasDuplicates(array) {
    var valuesSoFar = Object.create(null);
    for (var i = 0; i < array.length; ++i) {
        var value = array[i];
        if (value in valuesSoFar) {
            return true;
        }
        valuesSoFar[value] = true;
    }
    return false;
}

我們使用哈希表"valuesSoFar，其鍵是我們目前在數組中看到的值.我們使用 in 進行查找以查看是否已經發現了該值；如果是這樣，我們跳出循環并返回 true.

We use a "hash table" valuesSoFar whose keys are the values we've seen in the array so far. We do a lookup using in to see if that value has been spotted already; if so, we bail out of the loop and return true.

如果您需要的函數不僅僅適用于字符串值，則以下方法可以使用，但性能不佳；它是 O(n²) 而不是 O(n).

If you need a function that works for more than just string values, the following will work, but isn't as performant; it's O(n²) instead of O(n).

function hasDuplicates(array) {
    var valuesSoFar = [];
    for (var i = 0; i < array.length; ++i) {
        var value = array[i];
        if (valuesSoFar.indexOf(value) !== -1) {
            return true;
        }
        valuesSoFar.push(value);
    }
    return false;
}

不同之處在于我們對 valuesSoFar 使用數組而不是哈希表，因為 JavaScript 哈希表"(即對象)只有字符串鍵.這意味著我們失去了 in 的 O(1) 查找時間，而獲得了 indexOf 的 O(n) 查找時間.

The difference is simply that we use an array instead of a hash table for valuesSoFar, since JavaScript "hash tables" (i.e. objects) only have string keys. This means we lose the O(1) lookup time of in, instead getting an O(n) lookup time of indexOf.

這篇關于在 Javascript 中，如何檢查數組是否有重復值?的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！