Array=0821

//1.isPopOrder
public Boolean isPopOrder(int[] aNums, int[] bNums) {
    if (aNums == null || bNums == null||aNums.length!=bNums.length ) {
        return false;
    }
    int len=aNums.length;
    Stack<Integer> sk = new Stack<Integer>();
    int ai = 0;
    int bi = 0;
    while (bi < len) {
        if (ai==len) {return false;}
        int bAns=bNums[bi];
        //aNums[ai] dynamic add 
        if (sk.size() == 0) {
            sk.push(aNums[ai]);
            ai++;
        }
        while (ai < len) {
            //here use peek
            if (sk.peek()!= bValue) { 
                sk.push(aNums[ai]);
                ai++;  
            } else {
                break;
            }
        }
        sk.pop();//here use pop
        bi++;
    }
    if (sk.isEmpty() && ai == len && bi == len) {return true;}
    return false;
}

//2.reverseInt
public int reverse(int n) {
    //minValue can not be -minValue
    if (n == Integer.MIN_VALUE) {return 0;}
    if (n < 0) {return -reverse(-n);}
    int ans=0;
    while (n != 0) {
        //may exceed the max 
        if (ans > Integer.MAX_VALUE / 10) {return 0;}
        ans=ans * 10 + n % 10;n = n / 10;
    }
    return ans;
}

//3. isDuplicated in 1-n
public Boolean isDuplicated(int[] nums) {
    if (nums == null || nums.length == git 0) {return false;}
    for (int i = 0; i < nums.length; i++) {
        while (nums[i] != i) {
            if (nums[i] == nums[nums[i]]) {return true;} 
            int temp = nums[i];nums[i] = nums[nums[i]];nums[nums[i]] =temp;
        }
    }
    return defaultFlag;
}