744. Find Smallest Letter Greater Than Target

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"
找到數組裏邊的大於目標的最小值
思路以下，用二分查找找到目標便可，若是找不到則返回數組的第一位

public char nextGreatestLetter(char[] letters, char target) {
        int lo = 0, hi = letters.length;
        while (lo < hi) {
            int mi = lo + (hi - lo) / 2;
            if (letters[mi] <= target) lo = mi + 1;
            else hi = mi;
        }
        return letters[lo % letters.length];
    }

取mod是由於若是找不到lo最後會變成hi即letters.length

這種狀況下仍是返回第一個