binary search; lower bound; upper bound

theory/search_algorithm/binary_search.cpp

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+#include <iostream>
+
+int binary_search(int arr[], int l, int r, int x) {
+
+    while(l <= r) {
+        int mid = (l+r)/2;
+
+        if(arr[mid] < x) 
+            l=mid+1;
+        else if(arr[mid] > x)
+            r=mid-1;
+        else
+            return mid;
+
+    }
+
+    return EXIT_FAILURE;
+
+}
+
+int main(){
+
+    int arr[] = {1,2,3,4,5,6,7,8,9,10};
+    int n = 10;
+    if(binary_search(arr,0,n-1,6) != EXIT_FAILURE)
+        std::cout << "Element found at position: " << binary_search(arr,0,n-1,6) << std::endl;
+    else
+        std::cout << "Not-Found" << std::endl;
+
+
+}
+
+
+
+
+
+
+
+
+
+

theory/search_algorithm/frequency_count.cpp

@@ -0,0 +1,129 @@
+#include <iostream>
+#include <vector>
+
+// The most otimized solution
+/*
+
+We've to program 2 functions
+    -> lower bound
+    -> upper bound
+
+    to get the first occurency of the number and the last, the
+    answer'll be (Lo-Fo+1)
+
+*/
+
+int lower_bound(std::vector<int> arr, int key) {
+
+    int l = 0;
+    int r = arr.size() - 1;
+
+    int ans = -1;
+    while( l <= r) {
+
+        int mid = (l+r)/2;
+
+        if(arr[mid]==key) {
+            ans = mid;
+            r = mid - 1;
+        } else if (arr[mid] > key)
+            r=mid-1;
+        else
+            l=mid+1;
+
+    }
+
+    return ans;
+
+
+}
+
+int upper_bound(std::vector<int> arr, int key) {
+
+    int l = 0;
+    int r = arr.size() - 1;
+
+    int ans = -1;
+    while( l <= r) {
+
+        int mid = (l+r)/2;
+
+        if(arr[mid]==key) {
+            ans = mid;
+            l = mid + 1;
+        } else if (arr[mid] > key)
+            r=mid-1;
+        else
+            l=mid+1;
+
+    }
+
+    return ans;
+
+
+}
+
+int main(){
+
+    std::vector<int> arr = {0,1,1,1,1,2,2,2,3,4,4,5,10};
+    std::cout << (upper_bound(arr,1)-lower_bound(arr,1))+1 << std::endl;
+
+}
+
+
+//My solution
+/*
+
+
+int binary_search(int arr[], int l, int r, int x) {
+
+    while(l <= r) {
+        int mid = (l+r)/2;
+
+        if(arr[mid] < x)
+            l=mid+1;
+        else if(arr[mid] > x)
+            r=mid-1; 
+        else
+            return mid;
+    
+    }
+
+    return -1;
+
+}
+
+
+
+int main(){
+
+    int arr[] = {0,1,1,1,1,2,2,2,3,4,4,5,10};
+    int size = 12;
+
+    int id = binary_search(arr,0,size-1,2);
+    int i = id;
+    int count = 0;
+
+    if(id != -1) {
+        while(arr[i] == arr[id]) {
+            count++;
+            i++;
+        }
+    }
+
+    std::cout << count << std::endl;
+
+
+}
+*/
+
+
+
+
+
+
+
+
+
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+