算法——二分查找

二分查找

对于一个有序的可迭代序列，查找一个元素时，每次都猜中间的那个数，这样一次可以排除掉一半的数据

Python版本

def main(ary, item):

    low = 0
    high = len(ary) - 1

    while low <= high:
        mid_index = (low+high) // 2  # 中间索引位
        mid_value = ary[mid_index]  # 中间值

        if mid_value == item:
            return mid_index
        elif mid_value < item:
            low = mid_index + 1
        else:  # mid_value > item:
            high = mid_index - 1
    return None

ary = [1, 3, 4, 56, 78, 99]
print(main(ary, 3)) # 1

Java版本

public class More {

    public static void main(String[] args) {

        Integer[] ary = new Integer[] {1, 3, 4, 56, 78, 99};
        int item = 3;

        int low = 0;
        int high = ary.length - 1;

        while (low <= high) {
            int midIndex = (low + high) / 2;
            int midValue = ary[midIndex];

            if (midValue == item) {
                System.out.println(midIndex);
                break;
            } else if (midValue < item) {
                low = midIndex + 1;
            } else {
                high = midIndex - 1;
            }
        }
    }
}