题目
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.
Note:
0 <= pushed.length == popped.length <= 1000
0 <= pushed[i], popped[i] < 1000
pushed is a permutation of popped.
pushed and popped have distinct values.
题目地址
讲解
典型的栈的题目，练习此题，有助于加深对栈的理解和运用。
java 代码
class Solution {
public boolean validateStackSequences(int[] pushed, int[] popped) {
Stack<Integer> stack = new Stack<>();
int index=0;
for(int i=0;i<popped.length;i++){
if(stack.isEmpty()){
if(index<pushed.length){
stack.push(pushed[index++]);
}else{
return false;
}
}
while(popped[i]!=stack.peek()){
if(index<pushed.length){
stack.push(pushed[index++]);
}else{
return false;
}
}
stack.pop();
}
return true;
}
}