Question

我有阵列{1,2,3,4,4,4,5} 我希望我的函数返回索引为4。例如：4位于4,5,6位置

public void binarySearch(int value){ 
sort();  // sorting the array
int index=-1;
int lower=0;
int upper=count-1;
while(lower<=upper){
    int middle=(lower+upper)/2;

    if(value==array[middle]){
        index=middle;
        System.out.println(value+ " found at location "+(index+1));
        break;
        }
    else if(value<array[middle]){
        upper=middle-1;

    }
    else lower=middle+1;

}

}

Answer 1

这不太难。我们知道因为列表已经排序，所以我们所有的索引都是连续的（彼此相邻）。所以一旦我们找到了一个，我们只需要在两个方向上遍历列表，找出其他索引也匹配。

public static void binarySearch(int value){
    sort();
    int index = -1;
    int lower = 0;
    int upper = array.length - 1;
    while(lower <= upper){
        // The same as your code
    }

    // Create a list of indexes
    final List<Integer> indexes = new LinkedList<>();
    // Add the one we already found
    indexes.add(index);

    // Iterate upwards until we hit the end or a different value
    int current = index + 1;
    while (current < array.length && array[current] == value)
    {
        indexes.add(current);
        current++;
    }

    // Iterate downwards until we hit the start or a different value
    current = index - 1;
    while (current >= 0 && array[current] == value)
    {
        indexes.add(current);
        current--;
    }

    // Sort the indexes (do we care?)
    Collections.sort(indexes);

    for (int idx : indexes)
    {
        System.out.println(value + " found at " + (idx + 1));
    }
}

请记住，您实施的内容是已经二进制搜索。查找其他匹配索引的额外代码不属于二进制搜索的通常定义。

二进制搜索返回多个索引JAVA

1 个答案: