README_EN.md

946. Validate Stack Sequences

中文文档

Description

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.

Solutions

Python3

class Solution:
    def validateStackSequences(self, pushed: List[int], popped: List[int]) -> bool:
        stk, j, n = [], 0, len(popped)
        for x in pushed:
            stk.append(x)
            while stk and j < n and stk[-1] == popped[j]:
                stk.pop()
                j += 1
        return j == n

Java

class Solution {
    public boolean validateStackSequences(int[] pushed, int[] popped) {
        Deque<Integer> stk = new ArrayDeque<>();
        int j = 0, n = popped.length;
        for (int x : pushed) {
            stk.push(x);
            while (!stk.isEmpty() && j < n && stk.peek() == popped[j]) {
                stk.pop();
                ++j;
            }
        }
        return j == n;
    }
}

C++

class Solution {
public:
    bool validateStackSequences(vector<int>& pushed, vector<int>& popped) {
        int j = 0, n = popped.size();
        stack<int> stk;
        for (int x : pushed)
        {
            stk.push(x);
            while (!stk.empty() && j < n && stk.top() == popped[j])
            {
                stk.pop();
                ++j;
            }
        }
        return j == n;
    }
};

Go

func validateStackSequences(pushed []int, popped []int) bool {
	j, n := 0, len(popped)
	var stk []int
	for _, x := range pushed {
		stk = append(stk, x)
		for len(stk) > 0 && j < n && stk[len(stk)-1] == popped[j] {
			stk = stk[:len(stk)-1]
			j++
		}
	}
	return j == n
}

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