Minimum Lights to Activate

Author: anantkaushik

Python/Interviewbit/Arrays/minimum-lights-to-activate.py

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+"""
+Problem Link: https://www.interviewbit.com/problems/minimum-lights-to-activate/
+
+Problem Description
+There is a corridor in a Jail which is N units long. Given an array A of size N. The ith index of this array is 0 
+if the light at ith position is faulty otherwise it is 1.
+All the lights are of specific power B which if is placed at position X, it can light the corridor from [ X-B+1, X+B-1].
+Initially all lights are off.
+Return the minimum number of lights to be turned ON to light the whole corridor or -1 if the whole corridor cannot be lighted.
+
+Problem Constraints
+1 <= N <= 1000
+1 <= B <= 1000
+
+Input Format
+First argument is an integer array A where A[i] is either 0 or 1.
+Second argument is an integer B.
+
+Output Format
+Return the minimum number of lights to be turned ON to light the whole corridor or -1 if the whole corridor cannot be lighted.
+
+
+Example Input
+Input 1:
+A = [ 0, 0, 1, 1, 1, 0, 0, 1].
+B = 3
+
+Input 2:
+A = [ 0, 0, 0, 1, 0].
+B = 3
+
+Example Output
+Output 1:
+2
+
+Output 2:
+-1
+
+Example Explanation
+Explanation 1:
+In the first configuration, Turn on the lights at 3rd and 8th index.
+Light at 3rd index covers from [ 1, 5] and light at 8th index covers [ 6, 8].
+
+Explanation 2:
+In the second configuration, there is no light which can light the first corridor.
+"""
+class Solution:
+    # @param A : list of integers
+    # @param B : integer
+    # @return an integer
+    def solve(self, A, B):
+        n = len(A)
+        ans = 0
+        last = -1
+        while (last < n - 1):
+            pos = -1
+            end = max(-1,last - B + 1)
+            start = min(n-1,last + B)
+            for i in range( start, end , -1):
+                if (A[i] == 1 and i - B <= last):
+                    pos = i;
+                    break;
+                
+            
+            if (pos == -1):
+                return -1
+            
+            ans = ans + 1
+            last = pos + B - 1
+        
+        return ans