LeetCode 1441. 用栈操作构建数组

示例 1：
输入：target = [1,3], n = 3
输出：["Push","Push","Pop","Push"]
解释： 
读取 1 并自动推入数组 -> [1]
读取 2 并自动推入数组，然后删除它 -> [1]
读取 3 并自动推入数组 -> [1,3]

示例 2：
输入：target = [1,2,3], n = 3
输出：["Push","Push","Push"]

示例 3：
输入：target = [1,2], n = 4
输出：["Push","Push"]
解释：只需要读取前 2 个数字就可以停止。

示例 4：
输入：target = [2,3,4], n = 4
输出：["Push","Pop","Push","Push","Push"]
 
提示：
1 <= target.length <= 100
1 <= target[i] <= 100
1 <= n <= 100
target 是严格递增的

class Solution {
public:
    vector<string> buildArray(vector<int>& target, int n) {
    	vector<string> ans;
    	for(int i = 0, k = 1; k <= n && i < target.size(); ++k)
    	{
    		ans.push_back("Push");//数字k每次都需要push
    		if(target[i] != k)//不等于当前数的时候要pop
    			ans.push_back("Pop");
            else//相等的时候，target 后移 i++
                i++;
    	}
    	return ans;
    }
};