946. Validate Stack Sequences -----M

Given two sequences pushed and popped with distinct values, return true if and only if this could have been the result of a sequence of push and pop operations on an initially empty stack.

 

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:

• 0 <= pushed.length == popped.length <= 1000
• 0 <= pushed[i], popped[i] < 1000
• pushed is a permutation of popped.
• pushed and popped have distinct values.

 

A:

Just simulate the process on generating the popped result.

每次要想pop一个值。 需要操作stack来完成。

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

class Solution { public: bool validateStackSequences(vector<int>& pushed, vector<int>& popped) { stack<int> SS; int n = popped.size(); int start = 0; for(int i =0;i<n;i++){ int val = popped[i]; while(start<n && (SS.empty() || SS.top() != val)){ SS.push(pushed[start++]); } if(SS.empty() || SS.top() != val){ return false; } SS.pop(); } return true; } };