Update 37.Next Smaller Element.cpp

STACK/37.Next Smaller Element.cpp

@@ -1,61 +1,29 @@
-// A Stack based C++ program to find next
-// smaller element for all array elements
-#include <bits/stdc++.h>
+#include<bits/stdc++.h>
 using namespace std;
 
-// prints NSE for elements of array arr[] of size n
-
-void printNSE(int arr[], int n)
-{
-	stack<pair<int, int> > s;
-	vector<int> ans(n);
-
-	// iterate for rest of the elements
-	for (int i = 0; i < n; i++) {
-		int next = arr[i];
-
-		// if stack is empty then this element can't be NSE
-		// for any other element, so just push it to stack
-		// so that we can find NSE for it, and continue
-		if (s.empty()) {
-			s.push({ next, i });
-			continue;
-		}
-
-		// while stack is not empty and the top element is
-		// greater than next
-		// a) NSE for top is next, use top's index to
-		// maintain original order
-		// b) pop the top element from stack
-
-		while (!s.empty() && s.top().first > next) {
-			ans[s.top().second] = next;
-			s.pop();
-		}
-
-		// push next to stack so that we can find NSE for it
-
-		s.push({ next, i });
-	}
-
-	// After iterating over the loop, the remaining elements
-	// in stack do not have any NSE, so set -1 for them
-
-	while (!s.empty()) {
-		ans[s.top().second] = -1;
-		s.pop();
-	}
-
-	for (int i = 0; i < n; i++) {
-		cout << arr[i] << " ---> " << ans[i] << endl;
-	}
+vector<int> smallestGreaterEle(int arr[],int n){
+vector<int>v;
+stack<int>s;
+s.push(arr[n-1]);
+v.push_back(-1);
+for(int i=n-2;i>=0;i--){
+    while(!s.empty() and s.top()>=arr[i])
+    s.pop();
+    int ns=s.empty()?-1:s.top();
+    v.push_back(ns);
+    s.push(arr[i]);
+    }
+    reverse(v.begin(),v.end());
+return v;
 }
 
-// Driver program to test above functions
-int main()
-{
-	int arr[] = { 11, 13, 21, 3 };
-	int n = sizeof(arr) / sizeof(arr[0]);
-	printNSE(arr, n);
-	return 0;
+int main(){
+    int arr[]= {11, 13, 21, 3};
+    int n=4;
+    // arr[n];
+    vector<int>v=smallestGreaterEle(arr,n);
+    for(auto i: v)
+    cout<<i<<" ";
+
+    return 0;
 }