[Leetcode]330. Patching Array

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:
nums = [1, 3], n = 6
Return 1.

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

Example 3:
nums = [1, 2, 2], n = 5

Return 0.

题解：贪心。

class Solution {  public:      int minPatches(vector<int>& nums, int n) {          int len=nums.size();        long long pos=0,tmp=0,res=0;        for(long long i=1;i<=n;) {       //考察i是否需要添加。若i<=tmp（已有和）则不需要添加，否则添加i，更新已有和tmp，此时            while(pos<len&&nums[pos]<=i) {                //1~2*i-1一定都能表示                tmp+=nums[pos++];            }            if(tmp<i) {                res++;                tmp+=i;                i*=2;            }            else {                i=tmp+1;            }        }        return res;      }  };