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• 1004. 最大连续1的个数 III
• • 题意
  • 思路
  • 代码

1004. 最大连续1的个数 III

• 题意

• 思路

  • 二分
    遍历右端点，二分左端点，找到使这个区间0的个数$\le k$的最左边的左端点，可以用前缀和进行$O(1)$的判断

  • 双指针
    当二分的左端点随着右端点的移动而有序时，应该考虑可以用双指针来优化

• 代码

  • 二分

    class Solution:
        def longestOnes(self, nums, k) -> int:
            nums = [-1, *nums]
            b = [0] * len(nums)
    
            def check(l, r):
                if b[r] - b[l - 1] <= k:
                    return True
                return False
    
            def find(R):
                l, r = 1, len(b) - 1
                while l < r:
                    mid = l + r >> 1
                    if check(mid, R):
                        r = mid
                    else:
                        l = mid + 1
                return r
    
            for i in range(len(nums)):
                if nums[i] == 0:
                    b[i] = 1
                b[i] += b[i - 1]
            res = 0
            for i in range(1, len(nums)):
                L = find(i)
                if i == L and k == 0 and nums[i] == 0:
                    continue
                res = max(res, i - L + 1)
            return res
    
    

  • 双指针

    class Solution:
        def longestOnes(self, nums, k) -> int:
            n = len(nums)
            res, j, cnt = 0, 0, 0  #j左端点, cnt为0的个数
            for i in range(n):
                if nums[i] == 0:
                    cnt += 1
                while j <= i and cnt > k:
                    if nums[j] == 0:
                        cnt -= 1
                    j += 1
                res = max(res, i - j + 1)
            return res