leetcode

Max Consecutive Ones - Link

Question Description

Given a binary array nums, return the maximum number of consecutive 1’s in the array.

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Constraints

• 1 <= nums.length <= 10^5
• nums[i] is either 0 or 1

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Approach

Use a sliding window approach with two counters:

1. freq - tracks the current count of consecutive 1’s
2. count - tracks the maximum count seen so far

For each element in the array:

• If it’s 1, increment freq
• If it’s 0, reset freq to 0
• Update count with the maximum of count and freq

This approach works because we only need to track the current streak of consecutive 1’s and the maximum streak encountered. When we encounter a 0, the current streak breaks and we start counting from 0 again.

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Dry Run

Example Input: nums = [1,1,0,1,1,1]

Step-by-step execution:

• i=0, nums[0]=1, freq=1, count=1
• i=1, nums[1]=1, freq=2, count=2
• i=2, nums[2]=0, freq=0, count=2
• i=3, nums[3]=1, freq=1, count=2
• i=4, nums[4]=1, freq=2, count=2
• i=5, nums[5]=1, freq=3, count=3

Final Answer = 3

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Solution

class Solution {
    public int findMaxConsecutiveOnes(int[] nums) {
        int count=0;
        int freq=0;
        for(int i=0; i<nums.length; i++){
            if(nums[i]==1) freq++;
            else freq=0;
            count=Math.max(count, freq);
        }   
        return count;     
    }
}

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Time and Space Complexity

• Time Complexity: O(n) - single pass through the array
• Space Complexity: O(1) - constant space usage with just two integer variables
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