2100. Find Good Days to Rob the Bank, medium, prefix sums
- we have to check at every instance
- how many no.s will be smaller then current one.
- and how many no.s will be greater then the current one.
- brute force will give TLE
- therefore will have to store such values apriori i.e. use prefix, suffix.
Code
```cpp
vector goodDaysToRobBank(vector &security, int time) {
int n = security.size();
vector prefix(n, 0), suffix(n, 0);
for (int i = 1; i < n; i++)
if (security[i] <= security[i - 1])
prefix[i] = prefix[i - 1] + 1;
for (int i = n - 2; i >= 0; i--)
if (security[i] <= security[i + 1])
suffix[i] = suffix[i + 1] + 1;
vector ans;
for (int i = 0; i < n; i++)
if (prefix[i] >= time && suffix[i] >= time)
ans.push_back(i);
return ans;
}
```
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