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Find number of triangles that can be made by given sides of triangle

Outrageous Owl answered on March 28, 2022 Popularity 9/10 Helpfulness 1/10

answer Find number of triangles that can be made by given sides of triangle

Find number of triangles that can be made by given sides of triangle

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"""The time complexity can be greatly reduced using Two Pointer methods in just two nested loops.
Approach: First sort the array, and run a nested loop, fix an index and then try to fix an upper and lower index within which we can use all the lengths to form a triangle with that fixed index.
Algorithm:
Sort the array and then take three variables l, r and i, pointing to start, end-1 and array element starting from end of the array.
Traverse the array from end (n-1 to 1), and for each iteration keep the value of l = 0 and r = i-1
Now if a triangle can be formed using arr[l] and arr[r] then triangles can obviously formed 
from a[l+1], a[l+2]…..a[r-1], arr[r] and a[i], because the array is sorted , which can be directly calculated using (r-l). and then decrement the value of r and continue the loop till l is less than r
If a triangle cannot be formed using arr[l] and arr[r] then increment the value of l and continue the loop till l is less than r 
So the overall complexity of iterating 
through all array elements reduces.
"""
# Python implementation of the above approach
def CountTriangles( A):
 
    n = len(A);
 
    A.sort();
 
    count = 0;
     
    for i in range(n - 1, 0, -1):
        l = 0;
        r = i - 1;
        while(l < r):
            if(A[l] + A[r] > A[i]):
 
                # If it is possible with a[l], a[r]
                # and a[i] then it is also possible
                # with a[l + 1]..a[r-1], a[r] and a[i]
                count += r - l;
 
                # checking for more possible solutions
                r -= 1;
             
            else:
 
                # if not possible check for
                # higher values of arr[l]
                l += 1;
    print("No of possible solutions: ", count);
 
# Driver Code
if __name__ == '__main__':
 
    A = [ 4, 3, 5, 7, 6 ];
 
    CountTriangles(A);
     
# This code is contributed by PrinciRaj1992

Popularity 9/10 Helpfulness 1/10 Language python

Source: www.geeksforgeeks.org

Tags: find python triangle

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Contributed on Mar 28 2022

Outrageous Owl

0 Answers Avg Quality 2/10

Find number of triangles that can be made by given sides of triangle

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