LeetCode 946. 验证栈序列（栈）

示例 1：
输入：pushed = [1,2,3,4,5], popped = [4,5,3,2,1]
输出：true
解释：我们可以按以下顺序执行：
push(1), push(2), push(3), push(4), pop() -> 4,
push(5), pop() -> 5, pop() -> 3, pop() -> 2, pop() -> 1

示例 2：
输入：pushed = [1,2,3,4,5], popped = [4,3,5,1,2]
输出：false
解释：1 不能在 2 之前弹出。
 
提示：
0 <= pushed.length == popped.length <= 1000
0 <= pushed[i], popped[i] < 1000
pushed 是 popped 的排列。

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

class Solution {
public:
    bool validateStackSequences(vector<int>& pushed, vector<int>& popped) {
    	int i = 0, j = 0;
    	while(i < pushed.size())
    	{
    		if(pushed[i] == popped[j])
    		{
    			j++;
    			pushed.erase(pushed.begin()+i);
    			if(i != 0)
    				i--;
    		}
    		else if(i != pushed.size()-1)//不相等，且不在最后一个
    			i++;
    		else//不相等，且在最后一个
    			return false;
    	}
    	return true;
    }
};