
Problem Statement
In this problem, you are given a binary array nums
where each element is either 0
or 1
. The problem also provides an integer k
, which represents the maximum number of elements in the array that can be flipped from 0
to 1
. Your objective is to determine the maximum length of a subarray (a contiguous section of the array) that contains only 1
s after making no more than k
flips from 0
to 1
.
Examples
Example 1
Input:
nums = [1,1,1,0,0,0,1,1,1,1,0], k = 2
Output:
6
Explanation:
By flipping two 0s at positions 4 and 5, the subarray [1,1,1,1,1,1] is formed.
Example 2
Input:
nums = [0,0,1,1,0,0,1,1,1,0,1,1,0,0,0,1,1,1,1], k = 3
Output:
10
Explanation:
Flipping three 0s allows the longest subarray of 10 continuous 1s to form.
Constraints
1 <= nums.length <= 10^5
nums[i]
is either0
or1
0 <= k <= nums.length
Approach and Intuition
The goal is to find the length of the longest subarray containing only 1
s after flipping at most k
zeroes. A highly efficient way to solve this is by using the sliding window technique:
Initialize two pointers,
start
andend
, to define the window bounds.Use a counter
zero_count
to track how many0
s are in the current window.Expand the window by moving
end
forward.- If
nums[end]
is0
, incrementzero_count
. - If
zero_count
exceedsk
, shrink the window from the left by movingstart
forward until the number of zeroes is<= k
.
- If
At every step, compute the window size (
end - start + 1
) and update the maximum length seen so far.
This method ensures:
- All subarrays considered contain at most
k
zeroes. - Each element is visited at most twice: once by
end
and once bystart
.
As a result, the algorithm runs in O(n) time, where n
is the length of the input array — well within the problem’s constraints.
Solutions
- C++
- Java
- Python
class Solution {
public:
int maxConsecutiveOnes(vector<int>& arr, int maxFlips) {
int start = 0, end;
int len = arr.size();
for (end = 0; end < len; end++) {
if (arr[end] == 0) {
maxFlips--;
}
if (maxFlips < 0) {
maxFlips += 1 - arr[start];
start++;
}
}
return end - start;
}
};
This solution involves optimizing the length of the longest subarray that consists of consecutive 1's. This is possible by flipping a limited number of 0's to 1's, specified by maxFlips
. The implementation utilizes a sliding window approach to efficiently find the maximum length of such a subarray in a given array arr
.
Here's a breakdown of the approach:
- Initialize two pointers,
start
andend
, which represent the current window of numbers under consideration. - Iterate over the array using the
end
pointer, expanding the window to include new elements fromarr
. - If the current element is
0
, decrementmaxFlips
to account for flipping this zero to one. - If
maxFlips
becomes negative, it indicates that more than the allowed number of flips have been used. Adjust thestart
pointer to shrink the window from the left untilmaxFlips
is non-negative again. This ensures that the window only contains a valid number of flips. - The maximum length of the window that satisfies the condition is updated continuously by calculating the difference between the
end
andstart
pointers. - At the end of the loop, the length of the longest valid subarray is returned as
end - start
.
This code highlights efficient use of the sliding window technique to maintain a dynamically adjusting subarray that fulfills the flip condition, thus finding the answer in linear time relative to the size of arr
.
class Solution {
public int maxConsecutiveOnes(int[] arr, int flips) {
int start = 0, end;
for (end = 0; end < arr.length; end++) {
if (arr[end] == 0) {
flips--;
}
if (flips < 0) {
flips += 1 - arr[start];
start++;
}
}
return end - start;
}
}
To tackle the problem "Max Consecutive Ones III" in Java, follow these steps:
- Define the method
maxConsecutiveOnes
accepting an integer arrayarr
and an integerflips
, wherearr
represents a binary array andflips
denotes the maximum number of 0s that can be flipped to 1s. - Initialize two integer variables
start
andend
to zero.start
will track the beginning of the window, whileend
will extend the current window of consecutive ones. - Iterate through the array using
end
as the index for accessing each element in the array:- If the current element
arr[end]
at the indexend
is 0, decrementflips
as flipping a 0 to a 1 is considered. - If
flips
becomes negative (indicating more flips than allowed), adjust the window from the start:- Increment
flips
by 1 if the element at thestart
index is 0 (1 - arr[start]
does this adjustment). - Increment
start
to effectively reduce the window size, moving past the element that caused the extra flip.
- Increment
- If the current element
- Finally, calculate the maximum number of consecutive ones attainable by subtracting
start
fromend
. Since all elements have been checked when the loop concludes,end - start
gives the length of the longest segment with at mostflips
flipped zeros.
This logic efficiently expands and contracts a sliding window over the array to determine the maximum length of consecutive ones, including up to a specified number of zeros that could be flipped, culminating in the determination of the desired length.
class Solution:
def maxConsecutiveOnes(self, data: List[int], flips: int) -> int:
start = 0
for end in range(len(data)):
flips -= 1 - data[end]
if flips < 0:
flips += 1 - data[start]
start += 1
return end - start + 1
The provided Python code implements a solution that efficiently finds the maximum length of consecutive ones in a binary array after flipping at most flips
zero values to ones. This task is addressed using a sliding window technique, optimized to handle arrays and integer operations effectively. Here's how the code works:
- Initialize
start
to zero, marking the beginning of a sliding window. - Iterate over the array using
end
as the index. The window is extended fromstart
toend
. - Decrease the
flips
count each time a zero is encountered in the window. - If
flips
becomes negative (indicating that more thanflips
zeros have been flipped to sustain the current window), incrementstart
to shrink the window from the beginning and correct the flips balance—restoring flips only if a zero is passed over by thestart
pointer. - Calculate the length of the current window (
end - start + 1
) to update the potential maximum whenever necessary.
The code returns the maximum number of consecutive ones that can be obtained by flipping up to flips
zeros. This approach is efficient and handles edge cases with minimal computational overhead, leveraging linear time complexity relative to the size of the input array, thus providing a robust solution for large datasets.
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