744.Find Smallest Letter Greater Than Target

744. Find Smallest Letter Greater Than Target

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

直接找出當target大於給定目標值時的最小值，如果沒有，返回整個數組的最小值。 第一種方法：遞歸

class Solution {
public:
    char nextGreatestLetter(vector<char>& letters, char target) {
        char res='z'+1;
        for(auto c:letters)
            if(c>target )
                res=min(res,c);
        
        return res=='z'+1?nextGreatestLetter(letters, target-26): res ;
    }
};

执行用时 :24 ms, 在所有 C++ 提交中击败了22.61%的用户 内存消耗 :9 MB, 在所有 C++ 提交中击败了84.87%的用户

第二種方法，直接用一個變量保存最小值。

class Solution {
public:
    char nextGreatestLetter(vector<char>& letters, char target) {
        char res='z'+1;
        char minC=res;
        for(auto c:letters)
        {
            if(c>target )
                res=min(res,c);
            minC=min(minC,c);
        }
        
        return res=='z'+1?minC: res ;
    }
};

执行用时 :16 ms, 在所有 C++ 提交中击败了77.00%的用户 内存消耗 :9 MB, 在所有 C++ 提交中击败了88.11%的用户