Java 二分查找

public class Binary_Search{
    public static void main(String[] args) {
        System.out.println(binarySearch(new int[]{1, 3, 5, 6, 7, 9}, 6));
    }

    public static int binarySearch(int[] arr, int target) {
        int left = 0, right = arr.length;
        while (left <= right) {
            int mid = left + (right - left) / 2; // 防止越界
            if (arr[mid] == target) {
                // 如果数组中有多个target
                while (mid != 0 && arr[mid - 1] == arr[mid]) {
                    mid--;
                }
                return mid;
            } else if (arr[mid] > target) {
                right = mid - 1;
            } else {
                left = mid + 1;
            }
        }
        return -1;
    }
}