Package g1301_1400.s1375_number_of_times_binary_string_is_prefix_aligned

Class Solution

  • public class Solution
extends Object
    1375 - Number of Times Binary String Is Prefix-Aligned.

    Medium

    You have a 1-indexed binary string of length n where all the bits are 0 initially. We will flip all the bits of this binary string (i.e., change them from 0 to 1) one by one. You are given a 1-indexed integer array flips where flips[i] indicates that the bit at index i will be flipped in the ith step.

    A binary string is prefix-aligned if, after the ith step, all the bits in the inclusive range [1, i] are ones and all the other bits are zeros.

    Return the number of times the binary string is prefix-aligned during the flipping process.

    Example 1:

    Input: flips = [3,2,4,1,5]

    Output: 2

    Explanation: The binary string is initially “00000”.

    After applying step 1: The string becomes “00100”, which is not prefix-aligned.

    After applying step 2: The string becomes “01100”, which is not prefix-aligned.

    After applying step 3: The string becomes “01110”, which is not prefix-aligned.

    After applying step 4: The string becomes “11110”, which is prefix-aligned.

    After applying step 5: The string becomes “11111”, which is prefix-aligned.

    We can see that the string was prefix-aligned 2 times, so we return 2.

    Example 2:

    Input: flips = [4,1,2,3]

    Output: 1

    Explanation: The binary string is initially “0000”.

    After applying step 1: The string becomes “0001”, which is not prefix-aligned.

    After applying step 2: The string becomes “1001”, which is not prefix-aligned.

    After applying step 3: The string becomes “1101”, which is not prefix-aligned.

    After applying step 4: The string becomes “1111”, which is prefix-aligned.

    We can see that the string was prefix-aligned 1 time, so we return 1.

    Constraints:

    • n == flips.length
    • 1 <= n <= 5 * 104
    • flips is a permutation of the integers in the range [1, n].

    • Constructor Detail

      • Solution

        public Solution()

    • Method Detail

      • numTimesAllBlue

        public int numTimesAllBlue​(int[] flips)