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# Check if the tower of sight issue occurs or not

• Difficulty Level : Medium
• Last Updated : 02 Jun, 2021

Given four co-ordinates A, B, C and D where towers need to be constructed, the task is to check if the tower of sight issue occurs or not.

Tower of sight issue occurs if the towers at A or C lies in the line joining B and D or vice versa.

Examples:

Input: A = (0, 0), B = (0, -2), C = (2, 0), D = (0, 2)
Output: Yes
Explanation:
Tower A lies in the line joining B and D.
Input: A = (0, 0), B = (0, -2), C = (2, 0), D = (0, -5)
Output: No
Explanation:
No intersection occurs.

Approach:

• If A and C are parallel to the X-axis, check if B or D has y coordinate equal to that of A and C and x coordinate in between that of A and C.
• If A and C are parallel to the Y-axis, check if B or D has x coordinate equal to that of A and C and y coordinate in between that of A and C.
• Otherwise, check if B or D satisfies the line equation of A and C.
• Similarly follow the above three steps to check if A or C lies in between B or D.

Below code is the implementation of the above approach:

## C++

 `// C++ program to check if tower``// of sight issue occurs or not` `#include ``using` `namespace` `std;` `// Function to check if point p lies in``// between the line joining p1 and p2``int` `checkIntersection(pair<``int``, ``int``> p1,``                      ``pair<``int``, ``int``> p2,``                      ``pair<``int``, ``int``> p)``{``    ``int` `val;` `    ``// If parallel to X-axis``    ``if` `(p1.second == p2.second``        ``&& p1.second == p.second) {` `        ``if` `(p.first <= max(p1.first, p2.first)``            ``&& (p.first >= min(p1.first, p2.first)))` `            ``// Point p lies between p1 and p2``            ``return` `1;``    ``}` `    ``// If parallel to Y-axis``    ``if` `(p1.first == p2.first``        ``&& p1.first == p.first) {` `        ``if` `(p.second <= max(p1.second, p2.second)``            ``&& (p.second >= min(p1.second, p2.second)))` `            ``// Point p lies between p1 and p2``            ``return` `1;``    ``}` `    ``// If point p satisfies the equation``    ``// of line joining p1 and p2``    ``else` `{``        ``val = (p.second - p1.second)``                  ``* (p2.first - p1.first)``              ``- (p.first - p1.first)``                    ``* (p2.second - p1.second);` `        ``if` `(val == 0)``            ``if` `((p.first <= max(p1.first, p2.first)``                 ``&& (p.first >= min(p1.first, p2.first)))``                ``&& (p.second <= max(p1.second, p2.second)``                    ``&& (p.second >= min(p1.second, p2.second))))``                ``return` `1;``    ``}` `    ``return` `0;``}` `// Function to check if tower``// of sight issue occurred``void` `towerOfSight(pair<``int``, ``int``> a,``                  ``pair<``int``, ``int``> b,``                  ``pair<``int``, ``int``> c,``                  ``pair<``int``, ``int``> d)``{``    ``int` `flag = 0;` `    ``if` `(checkIntersection(a, c, b))` `        ``// B lies between AC``        ``flag = 1;` `    ``else` `if` `(checkIntersection(a, c, d))` `        ``// D lies between AC``        ``flag = 1;` `    ``else` `if` `(checkIntersection(b, d, a))` `        ``// A lies between BD``        ``flag = 1;` `    ``else` `if` `(checkIntersection(b, d, c))` `        ``// C lies between BD``        ``flag = 1;` `    ``flag ? cout << ``"Yes\n"``         ``: cout << ``"No\n"``;``}` `// Driver code``int` `main()``{``    ``// Point A``    ``pair<``int``, ``int``> a = { 0, 0 };` `    ``// Point B``    ``pair<``int``, ``int``> b = { 0, -2 };` `    ``// Point C``    ``pair<``int``, ``int``> c = { 2, 0 };` `    ``// Point D``    ``pair<``int``, ``int``> d = { 0, 2 };` `    ``towerOfSight(a, b, c, d);` `    ``return` `0;``}`

## Java

 `// Java program to check if tower``// of sight issue occurs or not``class` `GFG{` `static` `class` `pair``{``    ``int` `first, second;``    ``public` `pair(``int` `first, ``int` `second) ``    ``{``        ``this``.first = first;``        ``this``.second = second;``    ``}   ``}``  ` `// Function to check if point p lies in``// between the line joining p1 and p2``static` `int` `checkIntersection(pair p1,``                      ``pair p2,``                      ``pair p)``{``    ``int` `val;`` ` `    ``// If parallel to X-axis``    ``if` `(p1.second == p2.second``        ``&& p1.second == p.second) {`` ` `        ``if` `(p.first <= Math.max(p1.first, p2.first)``            ``&& (p.first >= Math.min(p1.first, p2.first)))`` ` `            ``// Point p lies between p1 and p2``            ``return` `1``;``    ``}`` ` `    ``// If parallel to Y-axis``    ``if` `(p1.first == p2.first``        ``&& p1.first == p.first) {`` ` `        ``if` `(p.second <= Math.max(p1.second, p2.second)``            ``&& (p.second >= Math.min(p1.second, p2.second)))`` ` `            ``// Point p lies between p1 and p2``            ``return` `1``;``    ``}`` ` `    ``// If point p satisfies the equation``    ``// of line joining p1 and p2``    ``else` `{``        ``val = (p.second - p1.second)``                  ``* (p2.first - p1.first)``              ``- (p.first - p1.first)``                    ``* (p2.second - p1.second);`` ` `        ``if` `(val == ``0``)``            ``if` `((p.first <= Math.max(p1.first, p2.first)``                 ``&& (p.first >= Math.min(p1.first, p2.first)))``                ``&& (p.second <= Math.max(p1.second, p2.second)``                    ``&& (p.second >= Math.min(p1.second, p2.second))))``                ``return` `1``;``    ``}`` ` `    ``return` `0``;``}`` ` `// Function to check if tower``// of sight issue occurred``static` `void` `towerOfSight(pair a,``                  ``pair b,``                  ``pair c,``                  ``pair d)``{``    ``int` `flag = ``0``;`` ` `    ``if` `(checkIntersection(a, c, b) == ``1``)`` ` `        ``// B lies between AC``        ``flag = ``1``;`` ` `    ``else` `if` `(checkIntersection(a, c, d) == ``1``)`` ` `        ``// D lies between AC``        ``flag = ``1``;`` ` `    ``else` `if` `(checkIntersection(b, d, a) == ``1``)`` ` `        ``// A lies between BD``        ``flag = ``1``;`` ` `    ``else` `if` `(checkIntersection(b, d, c) == ``1``)`` ` `        ``// C lies between BD``        ``flag = ``1``;`` ` `    ``System.out.print(flag==``1``?``"Yes\n"``:``"No\n"``);``}`` ` `// Driver code``public` `static` `void` `main(String[] args)``{``    ``// Point A``    ``pair a = ``new` `pair( ``0``, ``0` `);`` ` `    ``// Point B``    ``pair b = ``new` `pair( ``0``, -``2` `);`` ` `    ``// Point C``    ``pair c = ``new` `pair( ``2``, ``0` `);`` ` `    ``// Point D``    ``pair d = ``new` `pair( ``0``, ``2` `);`` ` `    ``towerOfSight(a, b, c, d);`` ` `}``}` `// This code is contributed by Rajput-Ji`

## Python3

 `# Python 3 program to check if tower``# of sight issue occurs or not`` ` `# Function to check if point p lies in``# between the line joining p1 and p2``def` `checkIntersection(p1,p2,p):`` ` `    ``# If parallel to X-axis``    ``if` `(p1[``1``] ``=``=` `p2[``1``]``        ``and` `p1[``1``] ``=``=` `p[``1``]):`` ` `        ``if` `(p[``0``] <``=` `max``(p1[``0``], p2[``0``])``            ``and` `(p[``0``] >``=` `min``(p1[``0``], p2[``0``]))):`` ` `            ``# Point p lies between p1 and p2``            ``return` `1`` ` `    ``# If parallel to Y-axis``    ``if` `(p1[``0``] ``=``=` `p2[``0``]``        ``and` `p1[``0``] ``=``=` `p[``0``]):`` ` `        ``if` `(p[``1``] <``=` `max``(p1[``1``], p2[``1``])``            ``and` `(p[``1``] >``=` `min``(p1[``1``], p2[``1``]))):`` ` `            ``# Point p lies between p1 and p2``            ``return` `1`` ` `    ``# If point p satisfies the equation``    ``# of line joining p1 and p2``    ``else` `:``        ``val ``=` `((p[``1``] ``-` `p1[``1``])``*``(p2[``0``] ``-` `p1[``0``])``              ``-` `(p[``0``] ``-` `p1[``0``])``                    ``*` `(p2[``1``] ``-` `p1[``1``]))`` ` `        ``if` `(val ``=``=` `0``):``            ``if` `((p[``0``] <``=` `max``(p1[``0``], p2[``0``])``                 ``and` `(p[``0``] >``=` `min``(p1[``0``], p2[``0``])))``                ``and` `(p[``1``] <``=` `max``(p1[``1``], p2[``1``])``                    ``and` `(p[``1``] >``=` `min``(p1[``1``], p2[``1``])))):``                ``return` `1`` ` `    ``return` `0`` ` `# Function to check if tower``# of sight issue occurred``def` `towerOfSight(a, b, c, d):``    ``flag ``=` `0`` ` `    ``if` `(checkIntersection(a, c, b)):`` ` `        ``# B lies between AC``        ``flag ``=` `1`` ` `    ``elif` `(checkIntersection(a, c, d)):``        ``# D lies between AC``        ``flag ``=` `1`` ` `    ``elif` `(checkIntersection(b, d, a)):`` ` `        ``# A lies between BD``        ``flag ``=` `1`` ` `    ``elif` `(checkIntersection(b, d, c)):`` ` `        ``# C lies between BD``        ``flag ``=` `1`` ` `    ``if``(flag):``        ``print``(``"Yes"``)``    ``else``:``        ``print``(``"No"``)`` ` `# Driver code``if` `__name__ ``=``=` `"__main__"``:` `    ``# Point A``    ``a ``=` `[ ``0``, ``0` `]`` ` `    ``# Point B``    ``b ``=` `[ ``0``, ``-``2` `]`` ` `    ``# Point C``    ``c ``=` `[ ``2``, ``0` `]`` ` `    ``# Point D``    ``d ``=` `[ ``0``, ``2` `]`` ` `    ``towerOfSight(a, b, c, d)`` ` `# This code is contributed by chitranayal`

## C#

 `// C# program to check if tower``// of sight issue occurs or not``using` `System;` `class` `GFG{`` ` `class` `pair``{``    ``public` `int` `first, second;``    ``public` `pair(``int` `first, ``int` `second) ``    ``{``        ``this``.first = first;``        ``this``.second = second;``    ``}   ``}``   ` `// Function to check if point p lies in``// between the line joining p1 and p2``static` `int` `checkIntersection(pair p1,``                      ``pair p2,``                      ``pair p)``{``    ``int` `val;``  ` `    ``// If parallel to X-axis``    ``if` `(p1.second == p2.second``        ``&& p1.second == p.second) {``  ` `        ``if` `(p.first <= Math.Max(p1.first, p2.first)``            ``&& (p.first >= Math.Min(p1.first, p2.first)))``  ` `            ``// Point p lies between p1 and p2``            ``return` `1;``    ``}``  ` `    ``// If parallel to Y-axis``    ``if` `(p1.first == p2.first``        ``&& p1.first == p.first) {``  ` `        ``if` `(p.second <= Math.Max(p1.second, p2.second)``            ``&& (p.second >= Math.Min(p1.second, p2.second)))``  ` `            ``// Point p lies between p1 and p2``            ``return` `1;``    ``}``  ` `    ``// If point p satisfies the equation``    ``// of line joining p1 and p2``    ``else` `{``        ``val = (p.second - p1.second)``                  ``* (p2.first - p1.first)``              ``- (p.first - p1.first)``                    ``* (p2.second - p1.second);``  ` `        ``if` `(val == 0)``            ``if` `((p.first <= Math.Max(p1.first, p2.first)``                 ``&& (p.first >= Math.Min(p1.first, p2.first)))``                ``&& (p.second <= Math.Max(p1.second, p2.second)``                    ``&& (p.second >= Math.Min(p1.second, p2.second))))``                ``return` `1;``    ``}``  ` `    ``return` `0;``}``  ` `// Function to check if tower``// of sight issue occurred``static` `void` `towerOfSight(pair a,``                  ``pair b,``                  ``pair c,``                  ``pair d)``{``    ``int` `flag = 0;``  ` `    ``if` `(checkIntersection(a, c, b) == 1)``  ` `        ``// B lies between AC``        ``flag = 1;``  ` `    ``else` `if` `(checkIntersection(a, c, d) == 1)``  ` `        ``// D lies between AC``        ``flag = 1;``  ` `    ``else` `if` `(checkIntersection(b, d, a) == 1)``  ` `        ``// A lies between BD``        ``flag = 1;``  ` `    ``else` `if` `(checkIntersection(b, d, c) == 1)``  ` `        ``// C lies between BD``        ``flag = 1;``  ` `    ``Console.Write(flag==1?``"Yes\n"``:``"No\n"``);``}``  ` `// Driver code``public` `static` `void` `Main(String[] args)``{``    ``// Point A``    ``pair a = ``new` `pair( 0, 0 );``  ` `    ``// Point B``    ``pair b = ``new` `pair( 0, -2 );``  ` `    ``// Point C``    ``pair c = ``new` `pair( 2, 0 );``  ` `    ``// Point D``    ``pair d = ``new` `pair( 0, 2 );``  ` `    ``towerOfSight(a, b, c, d);``  ` `}``}` `// This code is contributed by Princi Singh`

## Javascript

 ``
Output:
`Yes`

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