zoukankan      html  css  js  c++  java
  • Leetcode: Max Consecutive Ones II(unsolved locked problem)

    Given a binary array, find the maximum number of consecutive 1s in this array if you can flip at most one 0.
    
    Example 1:
    Input: [1,0,1,1,0]
    Output: 4
    Explanation: Flip the first zero will get the the maximum number of consecutive 1s.
        After flipping, the maximum number of consecutive 1s is 4.
    Note:
    
    The input array will only contain 0 and 1.
    The length of input array is a positive integer and will not exceed 10,000
    Follow up:
    What if the input numbers come in one by one as an infinite stream? In other words, you can't store all numbers coming from the stream as it's too large to hold in memory. Could you solve it efficiently?

    未研究:

    The idea is to keep a window [l, h] that contains at most k zero

    The following solution does not handle follow-up, because nums[l] will need to access previous input stream
    Time: O(n) Space: O(1)

        public int findMaxConsecutiveOnes(int[] nums) {
            int max = 0, zero = 0, k = 1; // flip at most k zero
            for (int l = 0, h = 0; h < nums.length; h++) {
                if (nums[h] == 0)                                           
                    zero++;
                while (zero > k)
                    if (nums[l++] == 0)
                        zero--;                                     
                max = Math.max(max, h - l + 1);
            }                                                               
            return max;             
        }
    

    Now let's deal with follow-up, we need to store up to k indexes of zero within the window [l, h] so that we know where to move lnext when the window contains more than k zero. If the input stream is infinite, then the output could be extremely large because there could be super long consecutive ones. In that case we can use BigInteger for all indexes. For simplicity, here we will use int
    Time: O(n) Space: O(k)

        public int findMaxConsecutiveOnes(int[] nums) {                 
            int max = 0, k = 1; // flip at most k zero
            Queue<Integer> zeroIndex = new LinkedList<>(); 
            for (int l = 0, h = 0; h < nums.length; h++) {
                if (nums[h] == 0)
                    zeroIndex.offer(h);
                if (zeroIndex.size() > k)                                   
                    l = zeroIndex.poll() + 1;
                max = Math.max(max, h - l + 1);
            }
            return max;                     
        }
    

    Note that setting k = 0 will give a solution to the earlier version Max Consecutive Ones

    For k = 1 we can apply the same idea to simplify the solution. Here q stores the index of zero within the window [l, h] so its role is similar to Queue in the above solution

        public int findMaxConsecutiveOnes(int[] nums) {
            int max = 0, q = -1;
            for (int l = 0, h = 0; h < nums.length; h++) {
                if (nums[h] == 0) {
                    l = q + 1;
                    q = h;
                }
                max = Math.max(max, h - l + 1);
            }                                                               
            return max;             
        }
  • 相关阅读:
    课程总结
    第十四周课程总结&实验报告
    第十三周课程总结
    第十二周课程总结
    第十一周课程总结
    第十周课程总结
    第七次java实验报告
    第六次java实验报告
    第五次java实验报告
    第四次java实验报告
  • 原文地址:https://www.cnblogs.com/EdwardLiu/p/6396014.html
Copyright © 2011-2022 走看看