Added Span Problems under stack algorithms

Author: mohitmo

Stack Algorithms/Span Problem/C++/span.cpp

@@ -0,0 +1,39 @@
+// Span Problem 
+// Here we have to find span of every element in an array, i.e number of consecutive elements before that element (including that element also)
+// having values less than or equal to value of current element
+// Note: Span of every element will be atleast 1 
+
+
+#include<iostream>
+#include<stack>
+using namespace std;
+
+//function for span problem
+void spans(int *a, int n, int *span){
+    stack<int> s;  
+    
+    for(int i = 0; i<n; i++){
+        while(!s.empty() && a[i]>=a[s.top()]){
+            s.pop();
+        }
+        if(s.empty()){
+            span[i] = i+1;
+            s.push(i);
+        }
+        else{
+            span[i] = i-s.top();
+            s.push(i);
+        }
+   }
+   
+}
+
+//testing our span function
+int main(){
+    int a[] = {9,12,5,13};
+    int span[4];
+    stack<int> s;
+    spans(a,4,span);
+    for(int i = 0 ; i<4; i++) cout<<span[i]<<endl;
+    
+}