Coding

66. Plus One

2026-01-02 1 min read
#Array#Math
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題目敘述

You are given a large integer represented as an integer array digits, where each digits[i] is the ith digit of the integer. The digits are ordered from most significant to least significant in left-to-right order. The large integer does not contain any leading 0’s.

Increment the large integer by one and return the resulting array of digits.

Example 1

Input: digits = [1,2,3] Output: [1,2,4] Explanation: The array represents the integer 123. Incrementing by one gives 123 + 1 = 124. Thus, the result should be [1,2,4].

Example 2

Input: digits = [4,3,2,1] Output: [4,3,2,2] Explanation: The array represents the integer 4321. Incrementing by one gives 4321 + 1 = 4322. Thus, the result should be [4,3,2,2].

Example 3

Input: digits = [9] Output: [1,0] Explanation: The array represents the integer 9. Incrementing by one gives 9 + 1 = 10. Thus, the result should be [1,0].

解題思路

從陣列的最後面開始進行 +1:

  • 如果該數字為 0~8，將該數字 +1，回傳整個陣列。
  • 如果該數字為 9，將該數字記為 0，繼續向前一位的陣列數字 +1。

如果一直加到最前面的陣列數字都還是 9，我們就需要創建一個比原先傳入陣列還要大一位的陣列，將首位數字設為 1，其餘為 0。

Solution

class Solution {
    public int[] plusOne(int[] digits) {
        
        for(int i = digits.length - 1; i >= 0; i--) {
            if (digits[i] < 9) {
                digits[i]++;
                return digits;
            }
            digits[i] = 0;
        }

        int[] newNumber = new int[digits.length + 1];
        newNumber[0] = 1;
        return newNumber;
    }
}
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