Last Updated: 13 Sep, 2020
Bursting Balloons
Moderate
Asked in companies
You are given an array 'ARR' of N integers. Each integer represents the height of a balloon. So, there are N balloons lined up.
Your aim is to destroy all these balloons. Now, a balloon can only be destroyed if the player shoots its head. So, to do the needful, he/ she shoots an arrow from the left to the right side of the platform, from an arbitrary height he/she chooses. The arrow moves from left to right, at a chosen height ARR[i] until it finds a balloon. The moment when an arrow touches a balloon, the balloon gets destroyed and disappears and the arrow continues its way from left to right at a height decreased by 1. Therefore, if the arrow was moving at height ARR[i], after destroying the balloon it travels at height ARR[i]-1. The player wins this game if he destroys all the balloons in minimum arrows.
You have to return the minimum arrows required to complete the task.
Input Format:
The first line of input contains an integer N representing the size of the array.
The second line of input contains N space-separated integers representing the height of the balloons.
Output Format:
Return a single integer i.e. the count of the minimum number of arrows required to complete the task.
Note:
You are not required to print the output, it has already been taken care of. Just implement the function.
Constraints:
1 <= N <= 10^5
1 <= ARR[i] <= 10^9
Time Limit: 1sec
Approaches
We can see here that balloons need to be destroyed in a minimum number of arrows so we need to reuse the arrows, also it’s clear that we need a new arrow for every balloon which is not getting destroyed by any previous arrow.
So we can solve this problem greedily by adding a new arrow for every balloon which is not getting destroyed by existing arrows.
- We will use a map data structure that will store the height of fired arrows.
- Start a loop from i = 0 to i = N - 1 and for the i’th balloon if the map contains the value ARR[i] then it means this balloon will get hit by the previous arrow.
- Therefore decrease the count of ARR[i] in the map and if it becomes 0 remove the key from the map.
- Increase the count of ARR[i]-1 in the map because there is an arrow at this height available.
- If the map does not contain the ARR[i] then We will need to fire a new arrow to increase the count of ARR[i] in the map.
- Now at the end find the sum of all the arrows present in the map and return it.