LeetCode - Easy - 66. Plus One

Topic

Array

Description

https://leetcode.com/problems/plus-one/

Given a non-empty array of decimal digits representing a non-negative integer, increment one to the integer.

The digits are stored such that the most significant digit is at the head of the list, and each element in the array contains a single digit.

You may assume the integer does not contain any leading zero, except the number 0 itself.

Example 1:

Input: digits = [1,2,3]
Output: [1,2,4]
Explanation: The array represents the integer 123.

Example 2:

Input: digits = [4,3,2,1]
Output: [4,3,2,2]
Explanation: The array represents the integer 4321.

Example 3:

Input: digits = [0]
Output: [1]

Constraints:

• 1 <= digits.length <= 100
• 0 <= digits[i] <= 9

Analysis

按照加法思路，注意陣列元素全是9的情況。

Submission

public class PlusOne {
	//我寫的
	public int[] plusOne1(int[] digits) {
		boolean carry = true;

		for (int i = digits.length - 1; carry && i >= 0; i--) {
			digits[i] = (carry = ++digits[i] == 10) ? 0 : digits[i];
		}

		if (carry) {
			digits = new int[digits.length + 1];
			digits[0] = 1;
		}

		return digits;
	}

	//別人寫的
	public int[] plusOne2(int[] digits) {
		int n = digits.length;
		for (int i = n - 1; i >= 0; i--) {
			if (digits[i] < 9) {
				digits[i]++;
				return digits;
			}

			digits[i] = 0;
		}

		int[] newNumber = new int[n + 1];
		newNumber[0] = 1;

		return newNumber;
	}
}

Test

import static org.junit.Assert.*;
import org.junit.Test;

public class PlusOneTest {

	@Test
	public void test() {
		PlusOne obj = new PlusOne();

		assertArrayEquals(new int[] {1, 2, 4}, obj.plusOne1(new int[] {1, 2, 3}));
		assertArrayEquals(new int[] {4, 3, 2, 2}, obj.plusOne1(new int[] {4, 3, 2, 1}));
		assertArrayEquals(new int[] {1}, obj.plusOne1(new int[] {0}));
		assertArrayEquals(new int[] {1, 0, 0, 0}, obj.plusOne1(new int[] {9, 9, 9}));
		assertArrayEquals(new int[] {6, 7, 9, 0}, obj.plusOne1(new int[] {6, 7, 8, 9}));
		
		assertArrayEquals(new int[] {1, 2, 4}, obj.plusOne2(new int[] {1, 2, 3}));
		assertArrayEquals(new int[] {4, 3, 2, 2}, obj.plusOne2(new int[] {4, 3, 2, 1}));
		assertArrayEquals(new int[] {1}, obj.plusOne2(new int[] {0}));
		assertArrayEquals(new int[] {1, 0, 0, 0}, obj.plusOne2(new int[] {9, 9, 9}));
		assertArrayEquals(new int[] {6, 7, 9, 0}, obj.plusOne2(new int[] {6, 7, 8, 9}));
		
	}
}