Patching Array

Desicription

Given a sorted positive integer array nums and an integer n, add/patch elements to the array such that any number in 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:

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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:

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Input: nums = [1,5,10], n = 20
Output: 2
Explanation: The two patches can be [2, 4].

Example 3:

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Input: nums = [1,2,2], n = 5
Output: 0

Solution

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class Solution {
public:
    int minPatches(std::vector<int>& nums, int n) {
        int res = 0;
        int index = 0;
        long long miss = 1;
        while(miss <= n) {
            if(index < nums.size() && nums[index] <= miss) {
                miss += nums[index++];
            } else {
                miss += miss;
                res++;
            }
        }
        return res;
    }
};