题解 | #二分查找-II#

class Solution {
public:
int search(vector<int>& nums, int target) {
return(helper(nums, target, 0, nums.size() - 1));
}
int helper(vector<int>& nums, int &target, int left, int right) {
if(left > right || nums[left] > target || nums[right] < target) //边界检测
return -1;
if(nums[left] == target) //判断一个区间最左边的值是否为target
return left;
int mid = (left + right) / 2; //以中点分为两个区间
int l_i = helper(nums, target, left, mid); //递归得到左区间target的索引值
if(l_i != -1) //不为-1说明找到索引
return l_i;
return helper(nums, target, mid + 1, right); //若左区间没找到则找右区间
}
};</int></int>