二进制搜索找不到数组列表中的第一个值

Question

我已经弄清楚了，因为我一直在寻找该值是否等于中点并且该值是第一个值，它永远不会为真，那么二进制搜索如何设法找到第一个元素数组？

private int date_searcher(String date, ArrayList all_dates) {
    found = false;
    int mid_point = 0;
    int first_index = 0;
    int last_index = all_dates.size() - 1;

    try {
        find_date_parse = date_format.parse(date);
    } catch (ParseException e) {
        warning_disp.setText("Please input a date in the valid format");
        validation = false;
    }

    while (first_index <= last_index & found == false & validation == true) {
        mid_point = (first_index + last_index) / 2;

        try { //parses the date in the mid point index
            mid_point_parse = date_format.parse((String) all_dates.get(mid_point));
        } catch (ParseException e) {}

        if (mid_point_parse.equals(find_date_parse)) {
            found = true;

        } else if (mid_point_parse.after(find_date_parse)) {
            last_index = mid_point + 1;

        } else if (mid_point_parse.before(find_date_parse)) {

            first_index = mid_point - 1;

        }
    }
    return mid_point;
}

Answer 1

改变最后的指令如下last_index = mid_point + 1; ==> last_index = mid_point - 1; first_index = mid_point - 1; ==> first_index = mid_point + 1;

已解决问题，谢谢 g.momo

Answer 2

我没有检查，但我认为你应该改变这个：

        last_index = mid_point - 1;     

        
        first_index = mid_point + 1;

Answer 3

您的问题出在移动索引时的范围上。只需更改最后的说明如下：

last_index = mid_point + 1; ==> last_index = mid_point - 1;

first_index = mid_point - 1; ==> first_index = mid_point + 1;

二进制搜索找不到数组列表中的第一个值

Binary Search cannot find the first value in the array list

java

binary-search

data-structures