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-rw-r--r--min_num_remove_mountain_arr.cpp51
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diff --git a/min_num_remove_mountain_arr.cpp b/min_num_remove_mountain_arr.cpp
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-// 1671. Minimum Number of Removals to Make Mountain Array
-#include "leetcode.h"
-
-/*
- * you may recall that an array 'arr' is a mountain array if and only if
- * 'arr.length >= 3', there exists soome index 'i' with '0 < i < arr.length - 1'
- * such that 'arr[0] < arr[1] <... < arr[i - 1]' and 'arr[i] > arr[i + 1] > ...
- * > arr[length - 1]'. given an integer array 'nums', return the minimum number
- * of elements to remove to make 'nums' a mountain array
- */
-
-class Solution {
-public:
- int minimumMountainRemovals(vector<int> &nums) {
- int n = nums.size();
- vector<int> left(n), right(n), stk;
- for (int i = 0; i < n; i++) {
- if (stk.empty() || stk.back() < nums[i]) {
- stk.push_back(nums[i]);
- left[i] = stk.size();
- } else {
- auto iter = lower_bound(stk.begin(), stk.end(), nums[i]);
- *iter = nums[i];
- left[i] = iter - stk.begin() + 1;
- }
- }
- stk.clear();
- for (int i = n - 1; i >= 0; i--) {
- if (stk.empty() || stk.back() < nums[i]) {
- stk.push_back(nums[i]);
- right[i] = stk.size();
- } else {
- auto iter = lower_bound(stk.begin(), stk.end(), nums[i]);
- *iter = nums[i];
- right[i] = iter - stk.begin() + 1;
- }
- }
- int max_item = 0;
- for (int i = 0; i < n; i++)
- if (left[i] >= 2 && right[i] >= 2)
- max_item = max(max_item, left[i] + right[i] - 1);
- return n - max_item;
- }
-};
-
-int main() {
- Solution obj;
- vector<int> n1 = {1, 3, 1}, n2 = {2, 1, 1, 5, 6, 2, 3, 1};
- printf("%d\n", obj.minimumMountainRemovals(n1)); // expect: 0
- printf("%d\n", obj.minimumMountainRemovals(n2)); // expect: 3
-}