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MaximalRectangle.cpp
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// https://leetcode.com/problems/maximal-rectangle/description/
class Solution {
public:
vector<int> nextSmallerElement(vector<int> arr, int n) {
stack<int> s;
s.push(-1);
vector<int> ans(n);
for(int i=n-1; i>=0 ; i--) {
int curr = arr[i];
while(s.top() != -1 && arr[s.top()] >= curr)
{
s.pop();
}
//ans is stack ka top
ans[i] = s.top();
s.push(i);
}
return ans;
}
vector<int> prevSmallerElement(vector<int> arr, int n) {
stack<int> s;
s.push(-1);
vector<int> ans(n);
for(int i=0; i<n; i++) {
int curr = arr[i];
while(s.top() != -1 && arr[s.top()] >= curr)
{
s.pop();
}
//ans is stack ka top
ans[i] = s.top();
s.push(i);
}
return ans;
}
int largestRectangleArea(vector<int>& heights) {
int n= heights.size();
vector<int> next(n);
next = nextSmallerElement(heights, n);
vector<int> prev(n);
prev = prevSmallerElement(heights, n);
int area = INT_MIN;
for(int i=0; i<n; i++) {
int l = heights[i];
if(next[i] == -1) {
next[i] = n;
}
int b = next[i] - prev[i] - 1;
int newArea = l*b;
area = max(area, newArea);
}
return area;
}
int maximalRectangle(vector<vector<char>>& matrix) {
int maxi= INT_MIN;
vector<int> histogram(matrix[0].size(), 0);
for(auto i : matrix){
for(int j= 0; j<i.size(); j++){
if(i[j]=='1'){
histogram[j]+= 1;
}
else{
histogram[j]= 0;
}
}
maxi= max(maxi, largestRectangleArea(histogram));
}
return maxi;
}
};