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Merge pull request #51 from shazly333/master

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Add Ternary Search
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Christian Bender 2018-03-09 21:03:40 +01:00 committed by GitHub
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1 changed files with 19 additions and 116 deletions
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ternary_search.cpp
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/* int three_part_binary_search(int a[], int x, int low, int high){
* This is a divide and conquer algorithm. if (low < high){
* It does this by dividing the search space by 3 parts and int m1 = (low + high) / 3 + 1;
* using its property (usually monotonic property) to find int m2 = 2 * (low + high) / 3 + 1;
* the desired index.
* if (x == a[m1])
* Time Complexity : O(log3 n) return m1;
* Space Complexity : O(1) (without the array) else if (x == a[m2])
*/ return m2;
else if (x < a[m1])
#include <iostream> return three_part_binary_search(a, x, low, m1 - 1);
using namespace std; else if (x<a[m2])
return three_part_binary_search(a, x, m1 + 1, m2 - 1);
/* else if (x>a[m2])
* The absolutePrecision can be modified to fit preference but return three_part_binary_search(a, x, m2 + 1, high);
* it is recommended to not go lower than 10 due to errors that }
* may occur. else
* return -1;
* The value of _target should be decided or can be decided later }
* by using the variable of the function.
*/
#define _target 10
#define absolutePrecision 10
#define MAX 10000000
int N = 21;
int A[MAX] = {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,3,4,10};
/*
* get_input function is to receive input from standard IO
*/
void get_input()
{
// TODO: Get input from STDIO or write input to memory as done above.
}
/*
* This is the iterative method of the ternary search which returns the index of the element.
*/
int it_ternary_search(int left, int right, int A[],int target)
{
while (1)
{
if(left<right)
{
if(right-left < absolutePrecision)
{
for(int i=left;i<=right;i++)
if(A[i] == target) return i;
return -1;
}
int oneThird = (left+right)/3+1;
int twoThird = (left+right)*2/3+1;
if(A[oneThird] == target) return oneThird;
else if(A[twoThird] == target) return twoThird;
else if(target > A[twoThird]) left = twoThird+1;
else if(target < A[oneThird]) right = oneThird-1;
else left = oneThird+1, right = twoThird-1;
}
else return -1;
}
}
/*
* This is the recursive method of the ternary search which returns the index of the element.
*/
int rec_ternary_search(int left, int right, int A[],int target)
{
if(left<right)
{
if(right-left < absolutePrecision)
{
for(int i=left;i<=right;i++)
if(A[i] == target) return i;
return -1;
}
int oneThird = (left+right)/3+1;
int twoThird = (left+right)*2/3+1;
if(A[oneThird] == target) return oneThird;
if(A[twoThird] == target) return twoThird;
if(target < A[oneThird]) return rec_ternary_search(left, oneThird-1, A, target);
if(target > A[twoThird]) return rec_ternary_search(twoThird+1, right, A, target);
return rec_ternary_search(oneThird+1, twoThird-1, A, target);
}
else return -1;
}
/*
* ternary_search is a template function
* You could either use it_ternary_search or rec_ternary_search according to preference.
*/
void ternary_search(int N,int A[],int target)
{
cout << it_ternary_search(0,N-1,A,target) << '\t';
cout << rec_ternary_search(0,N-1,A,target) << '\t';
cout << '\n';
}
int main()
{
get_input();
ternary_search(N,A,_target);
return 0;
}