Today I have done leetcode's April LeetCoding Challenge with cpp.

April LeetCoding Challenge 13

Description

Validate Stack Sequences

Given two integer arrays pushed and popped each with distinct values, return true if this could have been the result of a sequence of push and pop operations on an initially empty stack, or false otherwise.

Example 1:

Input: pushed = [1,2,3,4,5], popped = [4,5,3,2,1]
Output: true
Explanation: We might do the following sequence:
push(1), push(2), push(3), push(4),
pop() -> 4,
push(5),
pop() -> 5, pop() -> 3, pop() -> 2, pop() -> 1

Example 2:

Input: pushed = [1,2,3,4,5], popped = [4,3,5,1,2]
Output: false
Explanation: 1 cannot be popped before 2.

Constraints:

• 1 <= pushed.length <= 1000
• 0 <= pushed[i] <= 1000
• All the elements of pushed are unique.
• popped.length == pushed.length
• popped is a permutation of pushed.

Solution

class Solution {
public:
  bool validateStackSequences(vector<int>& pushed, vector<int>& popped) {
    vector<int> st;
    int pos = 0;
    int len = pushed.size();
    for(int i = 0; i < len; ++i) {
      while(pos < len && (st.empty() || st.back() != popped[i])) {
        st.push_back(pushed[pos]);
        pos += 1;
      }
      if(st.back() != popped[i]) return false;;
      st.pop_back();
    }
    return true;
  }
};

// Accepted
// 151/151 cases passed (4 ms)
// Your runtime beats 97.31 % of cpp submissions
// Your memory usage beats 59.16 % of cpp submissions (15.4 MB)