more STACK based ques

using C++ STL Maximum area histogram (MAH) Maximum area of boolean matrix (MAH variation) Rainwater trapping problem Min stack ques in O(n) space Min stack ques in O(1) space

Author: amn2

stack/(10)MinStackO(1).cpp

@@ -0,0 +1,80 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+// Min stack implementation without using ss stack i.e. in O(1) space
+
+stack<int> s;
+int minEle;
+
+void push(int a) {
+
+if (s.size() == 0) { s.push(a); minEle = a; }
+
+else {
+
+if (a >= minEle) {
+s.push(a);
+}
+else {
+s.push(2 * a - minEle);
+minEle = a;
+}
+
+}
+return;
+}
+
+int pop() {
+int ans;
+if (s.size() == 0) return -1;
+
+else {
+if (s.top() >= minEle) {
+ans = s.top();
+s.pop();
+}
+else {
+minEle = 2 * minEle - s.top();
+ans = s.top();
+s.pop();
+}
+}
+
+return ans;
+}
+
+int top() {
+
+if (s.size() == 0) return -1;
+
+else {
+if (s.top() <= minEle) return minEle;
+else return s.top();
+}
+}
+
+int getMIN() {
+
+return s.size() == 0 ? -1 : minEle;
+}
+
+
+int main() {
+
+#ifndef ONLINE_JUDGE
+freopen("input.txt", "r", stdin);
+freopen("output.txt", "w", stdout);
+#endif
+
+push(18);
+push(19);
+push(29);
+push(15);
+pop();
+push(16);
+pop();
+pop();
+
+cout << getMIN() << endl;
+
+}

stack/(6)MAH.cpp

@@ -0,0 +1,62 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+// Maximum area histogram (nothing to do with cavities) just the rectangle area formed
+int main() {
+
+#ifndef ONLINE_JUDGE
+freopen("input.txt", "r", stdin);
+freopen("output.txt", "w", stdout);
+#endif
+
+int a[] = {2, 3, 3, 2};
+int n = sizeof(a) / sizeof(int);
+
+vector<int> left;
+vector<int> right;
+stack<pair<int, int>> s;
+stack<pair<int, int>> s1;
+
+// NSL
+for (int i = 0; i < n; i++) {
+
+if (s.size() == 0) left.push_back(-1);
+else if (s.size() > 0 && s.top().first < a[i]) {
+left.push_back(s.top().second);
+}
+else if (s.size() > 0 && s.top().first >= a[i]) {
+while (s.size() > 0 && s.top().first >= a[i]) {
+s.pop();
+}
+if (s.size() == 0) left.push_back(-1);
+else left.push_back(s.top().second);
+}
+s.push({a[i], i});
+}
+//NSR
+for (int i = n - 1; i >= 0; i--) {
+
+if (s1.size() == 0) right.push_back(n);
+else if (s1.size() > 0 && s1.top().first < a[i]) {
+right.push_back(s1.top().second);
+}
+else if (s1.size() > 0 && s1.top().first >= a[i]) {
+while (s1.size() > 0 && s1.top().first >= a[i]) {
+s1.pop();
+}
+if (s1.size() == 0) right.push_back(n);
+else right.push_back(s1.top().second);
+}
+s1.push({a[i], i});
+}
+reverse(right.begin(), right.end());
+
+int area = INT_MIN;
+int temp;
+for (int i = 0; i < n; i++) {
+temp = (right[i] - left[i] - 1) * a[i];
+area = max(area, temp);
+}
+cout << area;
+
+}

stack/(7)MaxBM.cpp

@@ -0,0 +1,90 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+// Maximum area of rectangle in a binary matrix
+int MAH(vector<int> a, int n) {
+vector<int> left;
+vector<int> right;
+stack<pair<int, int>> s;
+stack<pair<int, int>> s1;
+
+// NSL
+for (int i = 0; i < n; i++) {
+
+if (s.size() == 0) left.push_back(-1);
+else if (s.size() > 0 && s.top().first < a[i]) {
+left.push_back(s.top().second);
+}
+else if (s.size() > 0 && s.top().first >= a[i]) {
+while (s.size() > 0 && s.top().first >= a[i]) {
+s.pop();
+}
+if (s.size() == 0) left.push_back(-1);
+else left.push_back(s.top().second);
+}
+s.push({a[i], i});
+}
+//NSR
+for (int i = n - 1; i >= 0; i--) {
+
+if (s1.size() == 0) right.push_back(n);
+else if (s1.size() > 0 && s1.top().first < a[i]) {
+right.push_back(s1.top().second);
+}
+else if (s1.size() > 0 && s1.top().first >= a[i]) {
+while (s1.size() > 0 && s1.top().first >= a[i]) {
+s1.pop();
+}
+if (s1.size() == 0) right.push_back(n);
+else right.push_back(s1.top().second);
+}
+s1.push({a[i], i});
+}
+reverse(right.begin(), right.end());
+
+int area = INT_MIN;
+int temp;
+for (int i = 0; i < n; i++) {
+temp = (right[i] - left[i] - 1) * a[i];
+area = max(area, temp);
+}
+return area;
+}
+
+int main() {
+
+
+#ifndef ONLINE_JUDGE
+freopen("input.txt", "r", stdin);
+freopen("output.txt", "w", stdout);
+#endif
+
+int n;
+cin >> n;
+int a[n][n];
+
+vector<int> v;
+
+for (int i = 0; i < n; i++) {
+for (int j = 0; j < n; j++) {
+cin >> a[i][j];
+}
+}
+
+for (int j = 0; j < n; j++) {
+v.push_back(a[0][j]);
+}
+
+int ans = MAH(v, n);
+
+for (int i = 1; i < n; i++) {
+for (int j = 0; j < n; j++) {
+if (a[i][j] == 0) v[j] = 0;
+else v[j] = v[j] + a[i][j];
+}
+ans = max(ans, MAH(v, n));
+}
+
+cout << ans;
+
+}

stack/(8)RainwaterTrap.cpp

@@ -0,0 +1,42 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+// Rainwater trapping (total trapped water)
+
+int main() {
+
+#ifndef ONLINE_JUDGE
+freopen("input.txt", "r", stdin);
+freopen("output.txt", "w", stdout);
+#endif
+
+int n;
+cin >> n;
+int a[n];
+
+for (int i = 0; i < n; i++) {
+cin >> a[i];
+}
+
+int maxL[n];
+int maxR[n];
+
+maxL[0] = a[0];
+maxR[n - 1] = a[n - 1];
+
+for (int i = 1; i < n; i++) {
+maxL[i] = max(maxL[i - 1], a[i]);
+}
+
+for (int i = n - 2; i >= 0; i--) {
+maxR[i] = max(maxR[i + 1], a[i]);
+}
+
+int ans = 0;
+for (int i = 0; i < n; i++) {
+ans = ans + min(maxL[i], maxR[i]) - a[i];
+}
+
+cout << ans << endl;
+
+}

stack/(9)MinStackO(n).cpp

@@ -0,0 +1,54 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+// Min stack implementation using ss stack
+
+stack<int> s;
+stack<int> ss; //supporting stack
+
+void push(int a) {
+
+s.push(a);
+if (ss.size() == 0 || a <= ss.top()) {
+ss.push(a);
+}
+return;
+}
+
+int pop() {
+
+int val = s.top();
+s.pop();
+
+if (ss.top() == val) {
+ss.pop();
+}
+
+return val;
+}
+
+int getMIN() {
+
+return ss.size() == 0 ? -1 : ss.top();
+}
+
+
+int main() {
+
+#ifndef ONLINE_JUDGE
+freopen("input.txt", "r", stdin);
+freopen("output.txt", "w", stdout);
+#endif
+
+push(18);
+push(19);
+push(29);
+push(15);
+pop();
+push(16);
+pop();
+pop();
+
+cout << getMIN() << endl;
+
+}