Formatted question description: https://leetcode.ca/all/744.html

744. Find Smallest Letter Greater Than Target (Easy)

Given a list of sorted characters letters containing only lowercase letters, and given a target letter target, find the smallest element in the list that is larger than the given target.

Letters also wrap around. For example, if the target is target = 'z' and letters = ['a', 'b'], the answer is 'a'.

Examples:

Input:
letters = ["c", "f", "j"]
target = "a"
Output: "c"

Input:
letters = ["c", "f", "j"]
target = "c"
Output: "f"

Input:
letters = ["c", "f", "j"]
target = "d"
Output: "f"

Input:
letters = ["c", "f", "j"]
target = "g"
Output: "j"

Input:
letters = ["c", "f", "j"]
target = "j"
Output: "c"

Input:
letters = ["c", "f", "j"]
target = "k"
Output: "c"

Note:

  1. letters has a length in range [2, 10000].
  2. letters consists of lowercase letters, and contains at least 2 unique letters.
  3. target is a lowercase letter.

Solution 1.

// OJ: https://leetcode.com/problems/find-smallest-letter-greater-than-target/

// Time: O(NlogN)
// Space: O(1)
class Solution {
public:
    char nextGreatestLetter(vector<char>& letters, char target) {
        auto i = upper_bound(letters.begin(), letters.end(), target);
        return i == letters.end() ? letters[0] : *i;
    }
};

Java

  • class Solution {
        public char nextGreatestLetter(char[] letters, char target) {
            int length = letters.length;
            char lastLetter = letters[length - 1];
            if (lastLetter <= target)
                return letters[0];
            int index = binarySearch(letters, target);
            return letters[index];
        }
    
        public int binarySearch(char[] letters, char target) {
            target++;
            int low = 0, high = letters.length - 1;
            while (low <= high) {
                int mid = (high - low) / 2 + low;
                char c = letters[mid];
                if (c == target)
                    return mid;
                else if (c > target)
                    high = mid - 1;
                else
                    low = mid + 1;
            }
            return low;
        }
    }
    
  • // OJ: https://leetcode.com/problems/find-smallest-letter-greater-than-target/
    // Time: O(NlogN)
    // Space: O(1)
    class Solution {
    public:
        char nextGreatestLetter(vector<char>& letters, char target) {
            auto i = upper_bound(letters.begin(), letters.end(), target);
            return i == letters.end() ? letters[0] : *i;
        }
    };
    
  • class Solution(object):
        def nextGreatestLetter(self, letters, target):
            """
            :type letters: List[str]
            :type target: str
            :rtype: str
            """
            for letter in letters:
            ## 提交了之后发现不用使用ord,字符可以用'>''<'比较大小
                if ord(letter) > ord(target):
                    return letter
            return letters[0]
    

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