it uses a sliding window with at most one '0' and then count the window length

```
class Solution {
public:
int findMaxConsecutiveOnes(vector<int>& nums) {
int start=0, usedup=0, maxl=0;
for (int i=0; i<nums.size(); ++i) {
if (nums[i]==0) {
if (!usedup) usedup=1;
else {
while(nums[start] !=0) start++;
++start;
}
}
maxl = max(maxl, i-start+1);
}
return maxl;
}
};
```