Preparing for the intervies of FLAG and USDA

public class ArrayList {
    private int capacity;
    private int size;
    private int[] data;
    public ArrayList(int capacity_) {
        capacity = capacity_;
        size = 0;
        data = new int[capacity];
    }
    public int get(int index) {
        if (index < 0 || index >= size) {
            // throw Exception
            System.out.println("ArrayIndexOutOfBoundsException: " + index);
        }
        return data[index];
    }
    public void set(int index, int value) {
        if (index < 0 || index >= size) {
            System.out.println("ArrayIndexOutOfBoundsException: " + index);
        }
        data[index] = value;
    }
    public void add(int index, int value) {
        if (index < 0 || index > size) {
            System.out.println("ArrayIndexOutOfBoundsException: " + index);
        }
        if (size == capacity) {
            resize();
        }
        size++;
        for (int i = size - 1; i >= index + 1; --i) {
            data[i] = data[i - 1];
        }
        data[index] = value;
    }
    private void resize() {
        capacity *= 2;
        int[] tempData = new int[size];
        for (int i = 0; i < size; ++i) {
            tempData[i] = data[i];
        }
        data = new int[capacity];
        for (int i = 0; i < size; ++i) {
            data[i] = tempData[i];
        }
    }
    public void remove(int index) {
        if (index < 0 || index >= size) {
            System.out.println("ArrayIndexOutOfBoundsException: " + index);
        }
        size--;
        for (int i = index; i < size; ++i) {
            data[i] = data[i + 1];
        }
    }
    
    public static void main(String[] args) {
        int[] a = {1};
        System.out.println(a[-1]);
    }
}

1. Two Sum My Submissions QuestionEditorial Solution
Total Accepted: 247444 Total Submissions: 1017480 Difficulty: Easy
Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution.

Example:
Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].
UPDATE (2016/2/13):
The return format had been changed to zero-based indices. Please read the above updated description carefully.

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public class Solution {
    public int[] twoSum(int[] nums, int target) {
        int[] res = new int[2];
        if (null == nums || nums.length == 0) {
            return res;
        }
        HashMap<Integer, Integer> map = new HashMap();
        for (int i = 0; i < nums.length; ++i) {
            if (!map.containsKey(nums[i])) {
                map.put(target - nums[i], i);
            } else {
                res[0] = map.get(nums[i]);
                res[1] = i;
                break;
            }
        }
        return res;
    }
}
/**
 * All Error:
 * 1, Compile Error : Line 20: error: unclosed comment. because the space of ‘*‘‘ and ‘/‘‘ 
 * 2, map.add. carelessness
 */

if the recurrence equation is T(n) = aT(b/n) + n ^ c。

if logb a > c , T(n) = n ^ (logb a)

if logb a == c, T(n) = n ^ c * logn

if logb a < c , T(n) = n ^ c