[LeetCode] Largest Rectangle in Histogram

This link has a very neat code, which is rewritten below using stack since the

push

and

pop

operations of it are

O(1)

time, while the

pop_back

and

push_back

of

vector

tend to be more time-consuming. This is also verified by the running time of the code on the OJ:

stack

version is generally 4ms to 8ms faster than

vector

version.

class Solution {
public:
int largestRectangleArea(vector<int>& height) {
height.push_back(0);
int n = height.size(), area = 0;
stack<int> indexes;
for (int i = 0; i < n; i++) {
while (!indexes.empty() && height[indexes.top()] > height[i]) {
int h = height[indexes.top()]; indexes.pop();
int l = indexes.empty() ? -1 : indexes.top();
area = max(area, h * (i - l - 1));
}
indexes.push(i);
}
return area;
}
};

Moreover, it would be better to keep

height

unmodified. So we loop for

n + 1

times and manually set the

h = 0

when

i == n

. The code is as follows.

class Solution {
public:
int largestRectangleArea(vector<int>& height) {
int n = height.size(), area = 0, h, l;
stack<int> indexes;
for (int i = 0; i <= n; i++) {
while (i == n || (!indexes.empty() && height[indexes.top()] > height[i])) {
if (i == n && indexes.empty()) h = 0, i++;
else h = height[indexes.top()], indexes.pop();
l = indexes.empty() ? -1 : indexes.top();
area = max(area, h * (i - l - 1));
}
indexes.push(i);
}
return area;
}
};