[LeetCode] 81. Search in Rotated Sorted Array II

Follow up for "Search in Rotated Sorted Array":
What if duplicates are allowed?
Would this affect the run-time complexity? How and why?
Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand.
(i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2).
Write a function to determine if a given target is in the array.
The array may contain duplicates.

Thought process:
The idea is similar to "154. Find Minimum in Rotated Sorted Array". If duplicates are allowed, worst case run-time will increase to O(n). Think about a case where the array contains a bunch of 1s and one 0, and we're searching for 0. 
We eliminate the edge case where nums[left] == nums[right] at the beginning of the while loop. After that, the code is similar to the question where duplicates are not allowed. Pay attention to those <= and >= signs, because they do matter in some edge cases.

Solution:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
public class Solution {
    public boolean search(int[] nums, int target) {
        if (nums.length == 0) {
            return false;
        }
        
        int left = 0;
        int right = nums.length - 1;
        int first = nums[0];
        
        while (left + 1 < right) {
            if (nums[left] == nums[right]) {
                right--;
                continue;
            }
            
            int mid = left + (right - left) / 2;
            if (nums[mid] >= first) {
                if (nums[mid] < target || first > target) {
                    left = mid;
                } else {
                    right = mid;
                }
            } else {
                if (nums[mid] > target || first <= target) {
                    right = mid;
                } else {
                    left = mid;
                }
            }
        }
        
        if (nums[left] == target || nums[right] == target) {
            return true;
        } else {
            return false;
        }
    }
}

Time complexity:
Average case O(logn). Worst case O(n).
Location: Philadelphia, PA, USA

Comments

Post a Comment

Popular posts from this blog

[LeetCode] 714. Best Time to Buy and Sell Stock with Transaction Fee

Your are given an array of integers  prices , for which the  i -th element is the price of a given stock on day  i ; and a non-negative integer  fee  representing a transaction fee. You may complete as many transactions as you like, but you need to pay the transaction fee for each transaction. You may not buy more than 1 share of a stock at a time (ie. you must sell the stock share before you buy again.) Return the maximum profit you can make. Example 1: Input: prices = [1, 3, 2, 8, 4, 9], fee = 2 Output: 8 Explanation: The maximum profit can be achieved by: Buying at prices[0] = 1 Selling at prices[3] = 8 Buying at prices[4] = 4 Selling at prices[5] = 9 The total profit is ((8 - 1) - 2) + ((9 - 4) - 2) = 8. Note: 0 < prices.length <= 50000 . 0 < prices[i] < 50000 . 0 <= fee < 50000 . Thought process: Each day there are two options, buy or sell. Use two variables buy and sell to keep track of the max profit. Solutio...
Read more

[LeetCode] 269. Alien Dictionary

There is a new alien language which uses the latin alphabet. However, the order among letters are unknown to you. You receive a list of  non-empty  words from the dictionary, where  words are sorted lexicographically by the rules of this new language . Derive the order of letters in this language. Example 1: Given the following words in dictionary, [ "wrt", "wrf", "er", "ett", "rftt" ] The correct order is:  "wertf" . Example 2: Given the following words in dictionary, [ "z", "x" ] The correct order is:  "zx" . Example 3: Given the following words in dictionary, [ "z", "x", "z" ] The order is invalid, so return  "" . Note: You may assume all letters are in lowercase. You may assume that if a is a prefix of b, then a must appear before b in the given dictionary. If the order is invalid, return an empty string...
Read more

[LeetCode] 631. Design Excel Sum Formula

Your task is to design the basic function of Excel and implement the function of sum formula. Specifically, you need to implement the following functions: Excel(int H, char W):  This is the constructor. The inputs represents the height and width of the Excel form.  H  is a positive integer, range from 1 to 26. It represents the height.  W  is a character range from 'A' to 'Z'. It represents that the width is the number of characters from 'A' to  W . The Excel form content is represented by a height * width 2D integer array  C , it should be initialized to zero. You should assume that the first row of  C  starts from 1, and the first column of  C  starts from 'A'. void Set(int row, char column, int val):  Change the value at  C(row, column)  to be val. int Get(int row, char column):  Return the value at  C(row, column) . int Sum(int row, char column, List of Strings : numbers):  This function...
Read more