根据下述二分查找法，在排好序的数组 1，3，6，9，17，31，39，52，61，79 中查找数值 31 ，循环while (left <= right) 执行的次数为（ ）。

int binary_search(vector<int>& nums, int target) {

      int left = 0;

      int right = nums.size() - 1;

      while (left <= right) {

            int mid = left + (right - left) / 2;

            if (nums[mid] == target) {

                  return mid;

            }

            else if (nums[mid] < target) {

                  left = mid + 1;

            }

            else {

                  right = mid - 1;

            }

      }

      return -1; // 如果找不到目标元素，返回-1

}