Merge pull request deutranium#78 from swapnil-satpathy/master

Added code for Binary Search from Scratch in C

Author: deutranium

searchingAlgo/binarySearch/binarySearch_scratch.c

@@ -0,0 +1,220 @@
+#include <stdio.h>
+
+
+
+// The below function module implements binary_search functionality in an iterative manner.
+// If the element is found then it returns the index otherwise -1;
+int binary_search(int arr[],int l,int r,int x){
+	while(l<=r){
+
+		// This way of calculating mid removes the chances of overflow with respect to the size of integer.
+		int mid=l+(r-l)/2;
+		if(arr[mid] == x)
+			return mid;
+		else if(arr[mid]<x)
+			l=mid+1;
+		else
+			r=mid-1;
+
+
+	}
+	return -1;
+}
+
+/* 
+
+The below functionality finds the lower_bound of an element in an array.
+
+Lower_bound returns the index of first occurrence of an element if the element is present in the array.
+If the element is not present in the array, then returns the index of element just greater than the given element.
+If the index returned is same as the length of the array,
+then it means the element given is greater than all the elements in the array
+
+*/
+
+
+int lower_bound(int arr[],int l,int r,int x){
+	while(l<=r){
+		int mid=l+(r-l)/2;
+		
+		if(arr[mid]>=x)
+			r=mid;
+		else
+			l=mid+1;
+		if(l==r)
+			break;
+	}
+	return l;
+
+}
+
+
+/*
+The below functionality finds the upper_bound of an element in an array.
+
+Upper_bound returns the index of the next greater element present than the element x passed as in input.
+If the output is the length of the array, it means that the upper_bound element is not present in the array
+*/
+
+int upper_bound(int arr[],int l,int r,int x){
+	while(l<=r){
+		int mid=l+(r-l)/2;
+		
+		if(arr[mid]<=x)
+			l=mid+1;
+		else
+			r=mid;
+		if(l==r)
+			break;
+	}
+	return l;
+
+}
+
+/*
+The below functionality implements floor functionality, i.e 
+it returns the array element less than or equal to the input x.
+*/
+
+
+int floor_(int arr[],int l,int r,int x){
+	int res=-1;
+    while(l<=r){
+        int mid=l+(r-l)/2;
+        if(arr[mid]==x)
+            return mid;
+        else if(arr[mid]<x){
+            l=mid+1;
+            res=mid;
+        }
+        else{
+            r=mid-1;
+            
+        }
+            
+    }
+    return res;
+}
+
+
+/*
+The below functionality implements ceil functionality, i.e 
+it returns the array element greater than or equal to the input x.
+*/
+
+
+int ceil_(int arr[],int l,int r,int x){
+	int res=-1;
+    while(l<=r){
+        int mid=l+(r-l)/2;
+        if(arr[mid]==x)
+            return mid;
+        else if(arr[mid]>x){
+            r=mid-1;
+            res=mid;
+        }
+        else{
+            l=mid+1;
+            
+        }
+            
+    }
+    return res;
+}
+
+
+
+int main(){
+
+	printf("Enter the number of elements in the array\n");
+	int n;
+	scanf("%d",&n);
+
+	int arr[n];
+
+	int a;
+	printf("Enter the elements of the array in sorted manner\n");
+	for(int i=0;i<n;i++){
+		scanf("%d",&a);
+		arr[i]=a;
+	}
+	int choice;
+	int x;
+
+
+	while(1){
+	printf("Please enter the number to be operated upon(ex. to be searched)\n");
+	
+	scanf("%d",&x);
+
+	
+	printf("Please enter the functionality you want to be operated upon\n");
+	printf("1 for binary_search\n");
+	printf("2 for lower_bound\n");
+	printf("3 for upper_bound\n");
+	printf("4 for ceil\n");
+	printf("5 for floor\n");
+	printf("6 to exit\n");
+	scanf("%d",&choice);
+
+
+	if(choice == 1){
+
+	int index=binary_search(arr,0,n-1,x);
+	if(index == -1)
+		printf("The element %d is not present in the array\n", x);
+	else
+		printf("The element %d is present at index %d of the array\n", x,index);
+
+	printf("*************************************************\n");
+	printf("\n");
+	
+	}
+	else if(choice == 2){
+		int index=lower_bound(arr,0,n-1,x);
+		
+		printf("The Lower_bound of the element %d in the array is %d\n", x,index);
+		printf("*************************************************\n");
+		printf("\n");
+
+	}
+	else if(choice == 3){
+		int index=upper_bound(arr,0,n-1,x);
+		printf("The Upper_bound of the element %d in the array is %d\n", x,index);
+		printf("*************************************************\n");
+		printf("\n");
+		
+	}
+	else if(choice == 4){
+		int index=ceil_(arr,0,n-1,x);
+		if(index == -1 || index==n)
+			printf("The ceil of the array is not present in the array\n");
+
+		else
+			printf("The ceil of the element %d in the array is %d\n", x,arr[index]);
+		printf("*************************************************\n");
+		printf("\n");
+	}
+	else if(choice == 5){
+		int index=floor_(arr,0,n-1,x);
+
+		if(index == -1)
+			printf("The floor of the element is not present in the array\n");
+		else
+			printf("The floor of the element %d in the array is %d\n", x,arr[index]);
+		printf("*************************************************\n");
+		printf("\n");
+	}
+
+	else if(choice == 6){
+		printf("Bubyee\n");
+		break;
+	}
+	else{
+		printf("Please provide a valid choice\n");
+	}
+}
+
+	return 0;
+	}
+