LeetCode-in-Java

330. Patching Array

Hard

Given a sorted integer array nums and an integer n, add/patch elements to the array such that any number in the range [1, n] inclusive can be formed by the sum of some elements in the array.

Return the minimum number of patches required.

Example 1:

Input: nums = [1,3], n = 6

Output: 1

Explanation:

Combinations of nums are [1], [3], [1,3], which form possible sums of: 1, 3, 4.
Now if we add/patch 2 to nums, the combinations are: [1], [2], [3], [1,3], [2,3], [1,2,3].
Possible sums are 1, 2, 3, 4, 5, 6, which now covers the range [1, 6].
So we only need 1 patch. 

Example 2:

Input: nums = [1,5,10], n = 20

Output: 2

Explanation: The two patches can be [2, 4].

Example 3:

Input: nums = [1,2,2], n = 5

Output: 0

Constraints:

• 1 <= nums.length <= 1000
• 1 <= nums[i] <= 104
• nums is sorted in ascending order.
• 1 <= n <= 231 - 1

Solution

public class Solution {
    public int minPatches(int[] nums, int n) {
        int res = 0;
        long sum = 0;
        int i = 0;
        while (sum < n) {
            // required number
            long req = sum + 1;
            if (i < nums.length && nums[i] <= req) {
                sum += nums[i++];
            } else {
                sum += req;
                res++;
            }
        }
        return res;
    }
}

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