剑指 Offer 53 - I. 在排序数组中查找数字 I

题目链接

53 - I. 在排序数组中查找数字 I

思路分析

利用二分查找即可。

class Solution {
public:
    int search(vector<int>& nums, int target) {
        std::ios::sync_with_stdio(false);
        if(nums.empty()) return 0;
        int l = 0, r = nums.size() - 1;
        while(l < r){
            int mid = (l + r) / 2;
            if(nums[mid] >= target) r = mid;
            else l = mid + 1;
        }
        if(nums[l] != target) return {0};
        else{
            int res = l;
            l = 0, r = nums.size() - 1;
            while(l < r){
                int mid = (l + r + 1) / 2;
                if(nums[mid] <= target) l = mid;
                else r = mid - 1;
            }
            return l - res + 1;
        }
    }
};