
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 1s 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 <= 10^5nums[i]is either0or10 <= k <= nums.length
Approach and Intuition
The goal is to find the length of the longest subarray containing only 1s after flipping at most k zeroes. A highly efficient way to solve this is by using the sliding window technique:
Initialize two pointers,
startandend, to define the window bounds.Use a counter
zero_countto track how many0s are in the current window.Expand the window by moving
endforward.- If
nums[end]is0, incrementzero_count. - If
zero_countexceedsk, shrink the window from the left by movingstartforward 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
kzeroes. - Each element is visited at most twice: once by
endand 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,
startandend, which represent the current window of numbers under consideration. - Iterate over the array using the
endpointer, expanding the window to include new elements fromarr. - If the current element is
0, decrementmaxFlipsto account for flipping this zero to one. - If
maxFlipsbecomes negative, it indicates that more than the allowed number of flips have been used. Adjust thestartpointer to shrink the window from the left untilmaxFlipsis 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
endandstartpointers. - 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
maxConsecutiveOnesaccepting an integer arrayarrand an integerflips, wherearrrepresents a binary array andflipsdenotes the maximum number of 0s that can be flipped to 1s. - Initialize two integer variables
startandendto zero.startwill track the beginning of the window, whileendwill extend the current window of consecutive ones. - Iterate through the array using
endas the index for accessing each element in the array:- If the current element
arr[end]at the indexendis 0, decrementflipsas flipping a 0 to a 1 is considered. - If
flipsbecomes negative (indicating more flips than allowed), adjust the window from the start:- Increment
flipsby 1 if the element at thestartindex is 0 (1 - arr[start]does this adjustment). - Increment
startto 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
startfromend. Since all elements have been checked when the loop concludes,end - startgives the length of the longest segment with at mostflipsflipped 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
startto zero, marking the beginning of a sliding window. - Iterate over the array using
endas the index. The window is extended fromstarttoend. - Decrease the
flipscount each time a zero is encountered in the window. - If
flipsbecomes negative (indicating that more thanflipszeros have been flipped to sustain the current window), incrementstartto shrink the window from the beginning and correct the flips balance—restoring flips only if a zero is passed over by thestartpointer. - 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.