Question

962. Maximum Width Ramp

中文文档

Description

A ramp in an integer array nums is a pair (i, j) for which i < j and nums[i] <= nums[j]. The width of such a ramp is j - i.

Given an integer array nums, return _the maximum width of a ramp in _nums. If there is no ramp in nums, return 0.

 

Example 1:

Input: nums = [6,0,8,2,1,5]
Output: 4
Explanation: The maximum width ramp is achieved at (i, j) = (1, 5): nums[1] = 0 and nums[5] = 5.

Example 2:

Input: nums = [9,8,1,0,1,9,4,0,4,1]
Output: 7
Explanation: The maximum width ramp is achieved at (i, j) = (2, 9): nums[2] = 1 and nums[9] = 1.

 

Constraints:

• 2 <= nums.length <= 5 * 104
• 0 <= nums[i] <= 5 * 104

Solutions

Solution 1

class Solution:
  def maxWidthRamp(self, nums: List[int]) -> int:
    stk = []
    for i, v in enumerate(nums):
      if not stk or nums[stk[-1]] > v:
        stk.append(i)
    ans = 0
    for i in range(len(nums) - 1, -1, -1):
      while stk and nums[stk[-1]] <= nums[i]:
        ans = max(ans, i - stk.pop())
      if not stk:
        break
    return ans

class Solution {
  public int maxWidthRamp(int[] nums) {
    int n = nums.length;
    Deque<Integer> stk = new ArrayDeque<>();
    for (int i = 0; i < n; ++i) {
      if (stk.isEmpty() || nums[stk.peek()] > nums[i]) {
        stk.push(i);
      }
    }
    int ans = 0;
    for (int i = n - 1; i >= 0; --i) {
      while (!stk.isEmpty() && nums[stk.peek()] <= nums[i]) {
        ans = Math.max(ans, i - stk.pop());
      }
      if (stk.isEmpty()) {
        break;
      }
    }
    return ans;
  }
}

class Solution {
public:
  int maxWidthRamp(vector<int>& nums) {
    int n = nums.size();
    stack<int> stk;
    for (int i = 0; i < n; ++i) {
      if (stk.empty() || nums[stk.top()] > nums[i]) stk.push(i);
    }
    int ans = 0;
    for (int i = n - 1; i; --i) {
      while (!stk.empty() && nums[stk.top()] <= nums[i]) {
        ans = max(ans, i - stk.top());
        stk.pop();
      }
      if (stk.empty()) break;
    }
    return ans;
  }
};

func maxWidthRamp(nums []int) int {
  n := len(nums)
  stk := []int{}
  for i, v := range nums {
    if len(stk) == 0 || nums[stk[len(stk)-1]] > v {
      stk = append(stk, i)
    }
  }
  ans := 0
  for i := n - 1; i >= 0; i-- {
    for len(stk) > 0 && nums[stk[len(stk)-1]] <= nums[i] {
      ans = max(ans, i-stk[len(stk)-1])
      stk = stk[:len(stk)-1]
    }
    if len(stk) == 0 {
      break
    }
  }
  return ans
}