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#ifdef LOCAL
#include <bits/stdc++.h>
using namespace std;
// tree node stuff here...
#endif
static int __initialSetup = []()
{
std::ios::sync_with_stdio(false);
cin.tie(NULL);
return 0;
}
();
class Solution
{
public:
// int trap(vector<int> &height)
// {
// // brute force: for every position, ...
// int sz = height.size();
// if (sz == 0)
// return 0;
// int ans = 0;
// for (int i = 1; i < sz - 1; i++) {
// int l = INT_MIN, r = INT_MIN;
// for (int j = 0; j < i; j++)
// l = max(l, height[j]);
// for (int j = i + 1; j < sz; j++)
// r = max(r, height[j]);
// int diff = min(l, r) - height[i];
// if (diff > 0)
// ans += diff;
// }
// return ans;
// }
int trap(vector<int> &height)
{
// brute force: for every position, ...
// l/r max can be precomputed
int sz = height.size();
if (sz == 0)
return 0;
int ans = 0;
int lmx[sz], rmx[sz];
memset(lmx, 0, sizeof(lmx));
lmx[0] = height[0];
memset(rmx, 0, sizeof(rmx));
rmx[sz - 1] = height[sz - 1];
for (int i = 1; i < sz; i++)
lmx[i] = max(lmx[i - 1], height[i]);
for (int i = sz - 2; i >= 0; i--)
rmx[i] = max(rmx[i + 1], height[i]);
for (int i = 1; i < sz - 1; i++) {
int diff = min(lmx[i], rmx[i]) - height[i];
if (diff > 0)
ans += diff;
}
return ans;
}
};
#ifdef LOCAL
int main()
{
return 0;
}
#endif
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