Description

Search in Rotated Sorted Array II

Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand.

(i.e., [0,0,1,2,2,5,6] might become [2,5,6,0,0,1,2]).

You are given a target value to search. If found in the array return true, otherwise return false.

Example 1:

Input: nums = [2,5,6,0,0,1,2], target = 0
Output: true

Example 2:

Input: nums = [2,5,6,0,0,1,2], target = 3
Output: false

Follow up:

  • This is a follow up problem to Search in Rotated Sorted Array, where nums may contain duplicates.
  • Would this affect the run-time complexity? How and why?

Solution

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class Solution {
 public:
    bool search(const std::vector<int>& nums, int target) {
        int l = 0;
        int r = nums.size() - 1;
        int mid, lnum, mnum, rnum;

        while (l <= r) {
            mid = l + (r - l)/2;

            lnum = nums.at(l);
            mnum = nums.at(mid);
            rnum = nums.at(r);

            // 一次判断三个数
            if (mnum == target || lnum == target || rnum == target) {
                return true;
            } else if (lnum < mnum) {
                // lnum < mnum 表示左边有序，那么判断target是否落在左边
                if (target < mnum && target >= lnum) {
                    r = mid - 1;
                } else {
                    l = mid + 1;
                }
            } else if (rnum > mnum) {
                // rnum > mnum 表示右边有序，那么判断target是否落在右边
                if (target > mnum && target <= rnum) {
                    l = mid + 1;
                } else {
                    r = mid - 1;
                }
            } else {
                // 收紧区域
                r--, l++;
            }
        }

        return false;
    }
};

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