Validate Stack Sequence 验证栈序列
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.
给了2个序列的入栈，出栈，按照2个栈的顺序，判断是否能将这个栈元素完全处理完。
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
思路
既然是栈，要出栈肯定是栈顶元素，或者就是下一个要入栈的元素。除了这2个情况，其他肯定不可能。
按照popped数组，扫描pushed数组，一个个入栈
public boolean validateStackSequences(int[] pushed, int[] popped) {
Stack<Integer> s = new Stack<>();
int j=0;
for (int i = 0; i < popped.length; i++) {
//focus on out stack,
//if popped stack top not equal pushed e ,push e until find e equal poped top
//then s.pop,
while (j<pushed.length&&(!s.isEmpty()||s.peek()!=popped[i])){
s.push(pushed[j]);
j+=1;
}
if (s.peek()!=popped[i]){
return false;
}
s.pop();
}
return true;
}
Tag
stack