Merge pull request ephremdeme#356 from amn2/stack

Stack based ques and solutions added using C++ STL

Author: Kanhakhatri065

stack/(1)NGR.cpp

@@ -0,0 +1,59 @@
+#include<bits/stdc++.h>
+using namespace std;
+typedef long long ll;
+#define mod 1000000007
+#define endl "\n"
+
+vector<int> v;
+stack<int> s;
+
+// Nearest Greater to Right - NGR
+void solve(int a[], int n) {
+
+for (int i = n - 1; i >= 0; i--) {
+
+if (s.size() == 0) {
+v.push_back(-1);
+}
+
+else if (s.size() > 0 && s.top() > a[i]) {
+v.push_back(s.top());
+}
+else if (s.size() > 0 && s.top() <= a[i]) {
+while (s.size() > 0 && s.top() <= a[i]) {
+s.pop();
+}
+
+if (s.size() == 0) v.push_back(-1);
+else v.push_back(s.top());
+}
+
+s.push(a[i]);
+
+}
+
+}
+
+
+int main()
+{
+
+ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
+
+#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];
+solve(a, n);
+
+reverse(v.begin(), v.end());
+for (int i = 0; i < n; i++) cout << v[i] << " ";
+
+}
+

stack/(2)NGL.cpp

@@ -0,0 +1,59 @@
+#include<bits/stdc++.h>
+using namespace std;
+typedef long long ll;
+#define mod 1000000007
+#define endl "\n"
+
+vector<int> v;
+stack<int> s;
+
+// Nearest Greater to left - NGL
+void solve(int a[], int n) {
+
+for (int i = 0; i < n; i++) {
+
+if (s.size() == 0) {
+v.push_back(-1);
+}
+
+else if (s.size() > 0 && s.top() > a[i]) {
+v.push_back(s.top());
+}
+else if (s.size() > 0 && s.top() <= a[i]) {
+while (s.size() > 0 && s.top() <= a[i]) {
+s.pop();
+}
+
+if (s.size() == 0) v.push_back(-1);
+else v.push_back(s.top());
+}
+
+s.push(a[i]);
+
+}
+
+}
+
+
+int main()
+{
+
+ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
+
+#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];
+solve(a, n);
+
+// reverse(v.begin(), v.end());
+for (int i = 0; i < n; i++) cout << v[i] << " ";
+
+}
+

stack/(3)NSR.cpp

@@ -0,0 +1,59 @@
+#include<bits/stdc++.h>
+using namespace std;
+typedef long long ll;
+#define mod 1000000007
+#define endl "\n"
+
+vector<int> v;
+stack<int> s;
+
+// Nearest Smaller to Right - NSR
+void solve(int a[], int n) {
+
+for (int i = n - 1; i >= 0 ; i--) {
+
+if (s.size() == 0) {
+v.push_back(-1);
+}
+
+else if (s.size() > 0 && s.top() < a[i]) {
+v.push_back(s.top());
+}
+else if (s.size() > 0 && s.top() >= a[i]) {
+while (s.size() > 0 && s.top() >= a[i]) {
+s.pop();
+}
+
+if (s.size() == 0) v.push_back(-1);
+else v.push_back(s.top());
+}
+
+s.push(a[i]);
+
+}
+
+}
+
+
+int main()
+{
+
+ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
+
+#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];
+solve(a, n);
+
+reverse(v.begin(), v.end());
+for (int i = 0; i < n; i++) cout << v[i] << " ";
+
+}
+

stack/(4)NSL.cpp

@@ -0,0 +1,59 @@
+#include<bits/stdc++.h>
+using namespace std;
+typedef long long ll;
+#define mod 1000000007
+#define endl "\n"
+
+vector<int> v;
+stack<int> s;
+
+// Nearest Smaller to Left - NSL
+void solve(int a[], int n) {
+
+for (int i = 0; i < n; i++) {
+
+if (s.size() == 0) {
+v.push_back(-1);
+}
+
+else if (s.size() > 0 && s.top() < a[i]) {
+v.push_back(s.top());
+}
+else if (s.size() > 0 && s.top() >= a[i]) {
+while (s.size() > 0 && s.top() >= a[i]) {
+s.pop();
+}
+
+if (s.size() == 0) v.push_back(-1);
+else v.push_back(s.top());
+}
+
+s.push(a[i]);
+
+}
+
+}
+
+
+int main()
+{
+
+ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
+
+#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];
+solve(a, n);
+
+// reverse(v.begin(), v.end());
+for (int i = 0; i < n; i++) cout << v[i] << " ";
+
+}
+

stack/(5)StockSpan.cpp

@@ -0,0 +1,60 @@
+#include<bits/stdc++.h>
+using namespace std;
+typedef long long ll;
+#define mod 1000000007
+#define endl "\n"
+
+//Stock Span Problem
+vector<int> v;
+stack<pair<int, int>> s;
+
+// Nearest Greater to Left - NGL
+void solve(int a[], int n) {
+
+for (int i = 0; i < n; i++) {
+
+if (s.size() == 0) {
+v.push_back(-1);
+}
+
+else if (s.size() > 0 && s.top().first > a[i]) {
+v.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) v.push_back(-1);
+else v.push_back(s.top().second);
+}
+
+s.push({a[i], i});
+
+}
+
+}
+
+
+int main()
+{
+
+ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
+
+#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];
+solve(a, n);
+
+// reverse(v.begin(), v.end());
+for (int i = 0; i < n; i++) cout << i - v[i] << " ";
+
+}
+