Description:

Given a characters array letters that is sorted in non-decreasing order and a character target, return the smallest character in the array that is larger than target.

Note that the letters wrap around.

For example, if target == ‘z’ and letters == [‘a’, ‘b’], the answer is ‘a’.

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/find-smallest-letter-greater-than-target

Solution_1

traverse all elements in array and find the smallest character in non-decreasing order sorted arrray

The results of my codes:

The smallest character in the array that is larger than d is f

The corresponding codes:

#include <iostream>
#include <vector>
#include <iomanip>

using std::cout;
using std::cin;
using std::endl;
using std::string;
using std::max;
using std::vector;
using std::setw;
char nextGreatestLetter(vector<char>& letters, char target);
int main()
{
	vector<char> letters{'c','f','j'};
	char target = 'd';
	char result = nextGreatestLetter(letters, target);
	cout << "The smallest character in the array that is larger than " << target << " is " << result << endl;
	return 0;
}

char nextGreatestLetter(vector<char>& letters, char target)
{
	for (char letter : letters){
		if (letter > target) return letter;
	}
	return letters[0];
}

Solution_2

==Just use binary search method to find the ==

The codes:

#include <iostream>
#include <vector>
#include <iomanip>
#include <bits/stdc++.h>

using std::cout;
using std::cin;
using std::endl;
using std::string;
using std::max;
using std::vector;
using std::setw;
//see whether num is self dividing or not
char nextGreatestLetter(vector<char>& letters, char target);
int main()
{
	vector<char> letters{'c','f','j'};
	char target = 'd';
	char result = nextGreatestLetter(letters, target);
	cout << "The smallest character in the array that is larger than " << target << " is " << result << endl;
	return 0;
}

char nextGreatestLetter(vector<char>& letters, char target)
{
	return target < letters.back() ? *upper_bound(letters.begin(), letters.end() - 1, target) : letters[0];
}