Java数组，查找重复项

Question

Java数组，查找重复项

我有一个数组，正在寻找副本。

duplicates = false;for(j = 0; j < zipcodeList.length; j++){
    for(k = 0; k < zipcodeList.length; k++){
        if (zipcodeList[k] == zipcodeList[j]){
            duplicates = true;
        }
    }}

但是，当没有副本时，此代码不能工作。为什么这么说？

Answer 1

让我们看看您的算法是如何工作的：an array of unique values:[1, 2, 3]check 1 == 1. yes, there is duplicate, assigning duplicate to true.check 1 == 2. no, doing nothing.check 1 == 3. no, doing nothing.check 2 == 1. no, doing nothing.check 2 == 2. yes, there is duplicate, assigning duplicate to true.check 2 == 3. no, doing nothing.check 3 == 1. no, doing nothing.check 3 == 2. no, doing nothing.check 3 == 3. yes, there is duplicate, assigning duplicate to true.更好的算法：for (j=0;j<zipcodeList.length;j++) {&nbsp; &nbsp; for (k=j+1;k<zipcodeList.length;k++) {&nbsp; &nbsp; &nbsp; &nbsp; if (zipcodeList[k]==zipcodeList[j]){ // or use .equals()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return true;&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }}return false;

Answer 2

您可以使用位图来提高大数组的性能。&nbsp;&nbsp;&nbsp;&nbsp;java.util.Arrays.fill(bitmap,&nbsp;false); &nbsp;&nbsp;&nbsp;&nbsp;for&nbsp;(int&nbsp;item&nbsp;:&nbsp;zipcodeList) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(!bitmap[item])&nbsp;bitmap[item]&nbsp;=&nbsp;true; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;else&nbsp;break;更新：这是我在过去的一个非常疏忽的回答，把它保存在这里仅供参考。你应该参考Andersoj的优秀作品回答.