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Commit b771202

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LeetCode problem: 744. Find Smallest Letter Greater Than Target
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  • src
    • main/java/com/borrelunde/leetcodesolutions/problem0744/findsmallestlettergreaterthantarget
    • test/java/com/borrelunde/leetcodesolutions/problem0744/findsmallestlettergreaterthantarget

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# 744. Find Smallest Letter Greater Than Target
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Difficulty: `Easy`
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Topics: `Array`, `Binary Search`
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You are given an array of characters `letters` that is sorted in **non-decreasing order**, and a character `target`.
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There are **at least two different characters** in `letters`.
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Return *the smallest character in `letters` that is lexicographically greater than `target`*. If such a character does
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not exist, return the first character in `letters`.
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**Example 1:**
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```text
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Input: letters = ["c","f","j"], target = "a"
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Output: "c"
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Explanation: The smallest character that is lexicographically greater than 'a' in letters is 'c'.
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```
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**Example 2:**
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```text
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Input: letters = ["c","f","j"], target = "c"
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Output: "f"
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Explanation: The smallest character that is lexicographically greater than 'c' in letters is 'f'.
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```
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**Example 3:**
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```text
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Input: letters = ["x","x","y","y"], target = "z"
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Output: "x"
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Explanation: There are no characters in letters that is lexicographically greater than 'z' so we return letters[0].
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```
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**Constraints:**
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- `2 <= letters.length <= 10^4`
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- `letters[i]` is a lowercase English letter.
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- `letters` is sorted in **non-decreasing** order.
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- `letters` contains at least two different characters.
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- `target` is a lowercase English letter.
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package com.borrelunde.leetcodesolutions.problem0744.findsmallestlettergreaterthantarget;
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/**
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* This is the solution to the LeetCode problem: 744. Find Smallest Letter
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* Greater Than Target
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*
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* @author Børre A. Opedal Lunde
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* @since 2024年01月29日
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*/
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public class Solution {
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public char nextGreatestLetter(char[] letters, char target) {
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int lowIndex = 0;
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int highIndex = letters.length - 1;
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// Binary search.
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while (lowIndex <= highIndex) {
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final int middleIndex = lowIndex + (highIndex - lowIndex) / 2;
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final char middleCharacter = letters[middleIndex];
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if (middleCharacter > target) {
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highIndex = middleIndex - 1;
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} else {
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lowIndex = middleIndex + 1;
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}
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}
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// After the search, the low index is the index of the smallest
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// greatest character. The only chance it isn't is if the index
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// surpasses the array and is out of bounds.
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// In that case, return the first character in letters.
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if (lowIndex >= letters.length) {
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return letters[0];
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}
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// Otherwise, return the character at its position.
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return letters[lowIndex];
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}
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}
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package com.borrelunde.leetcodesolutions.problem0744.findsmallestlettergreaterthantarget;
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import org.junit.jupiter.api.DisplayName;
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import org.junit.jupiter.api.Test;
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import org.junit.jupiter.params.ParameterizedTest;
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import org.junit.jupiter.params.provider.Arguments;
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import org.junit.jupiter.params.provider.MethodSource;
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import java.util.stream.Stream;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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/**
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* This is the test to the LeetCode problem: 744. Find Smallest Letter Greater
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* Than Target
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*
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* @author Børre A. Opedal Lunde
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* @since 2024年01月29日
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*/
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@DisplayName("Find Smallest Letter Greater Than Target")
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class SolutionTest {
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private final Solution solution = new Solution();
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@Test
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@DisplayName("Example one")
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void exampleOne() {
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char[] letters = {'c', 'f', 'j'};
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char target = 'a';
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char expected = 'c';
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char actual = solution.nextGreatestLetter(letters, target);
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assertEquals(expected, actual);
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}
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@Test
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@DisplayName("Example two")
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void exampleTwo() {
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char[] letters = {'c', 'f', 'j'};
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char target = 'c';
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char expected = 'f';
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char actual = solution.nextGreatestLetter(letters, target);
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assertEquals(expected, actual);
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}
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@Test
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@DisplayName("Example three")
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void exampleThree() {
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char[] letters = {'x', 'x', 'y', 'y'};
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char target = 'z';
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char expected = 'x';
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char actual = solution.nextGreatestLetter(letters, target);
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assertEquals(expected, actual);
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}
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@Test
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@DisplayName("Should return first letter when target is last element in array")
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void shouldReturnFirstLetterWhenTargetIsLastElementInArray() {
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char[] letters = {'a', 'b', 'c', 'd', 'f', 'g'};
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char target = 'g';
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char expected = 'a';
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char actual = solution.nextGreatestLetter(letters, target);
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assertEquals(expected, actual);
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}
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static Stream<Arguments> provideLettersWithTargetInMiddleButNotPresent() {
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return Stream.of(
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Arguments.of(new char[]{'b', 'd'}, 'c', 'd'),
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Arguments.of(new char[]{'a', 'b', 'd', 'e'}, 'c', 'd'),
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Arguments.of(new char[]{'m', 'n', 'p', 'q'}, 'o', 'p'),
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Arguments.of(new char[]{'n', 'n', 'p', 'p'}, 'o', 'p'),
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Arguments.of(new char[]{'a', 'b', 'x', 'y'}, 'c', 'x'),
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Arguments.of(new char[]{'c', 'f', 'j'}, 'd', 'f')
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);
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}
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@ParameterizedTest(name = "In {0} with target {1} should return {2}")
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@DisplayName("Should return smallest greater character when target is not in array")
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@MethodSource("provideLettersWithTargetInMiddleButNotPresent")
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void shouldReturnSmallestGreaterCharacterWhenTargetIsNotInArray(char[] letters, char target, char expected) {
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char actual = solution.nextGreatestLetter(letters, target);
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assertEquals(expected, actual);
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}
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}

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