原文：

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, and you may not use the same element twice.

Example:

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

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

解题：

package leetcode;

import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.Stack;

public class Demo1 {
    //暴力解题
    public static  int[] twoSum(int[] nums, int target) {
    	Stack<Integer> stack = new Stack<Integer>();
        for(int i=0; i<nums.length; i++)
        {
        	int tmp = nums[i];
        	stack.add(tmp);
        }
        while(stack.iterator().hasNext()) {
        	int i=0;
        	int[] temp = new int[2];
        	Integer peek = stack.peek();
        	for(int j=i+1;j<nums.length;j++)
        	{
        		int peek2 = nums[j];
        		int vv = peek2 + peek;
        		if(vv == target)
        		{
        			temp[0] = peek;
        			temp[1] = peek2;
            		System.out.println("输出数组：temp = ["+i+","+j+"]");
        		}
        	}
        	i++;
        	stack.pop();
        }
        return new int[] {};
    }
    //暴力解题
    public static  void twoSum1(int[] nums, int target) {
        for(int i = 0;i<nums.length;i++) {
        	int[] temp = new int[2];
        	Integer peek = nums[i];
        	for(int j=i+1;j<nums.length;j++)
        	{
        		int vv = nums[j] + peek;
        		if(vv == target)
        		{
        			temp[0] = peek;
        			temp[1] = nums[j];
            		System.out.println("输出数组：temp = ["+i+","+j+"]");
        		}
        	}
        }
    }
    //参考大佬的方法
    public static void twoSum3(int[] nums, int target) {
    	int[] temp = new int[2];
    	Map<Integer,Integer>  map = new HashMap();
    	for(int i= 0; i<nums.length; i++)
    	{
    		if(map.containsKey(nums[i]))
    		{
    			temp[0] = map.get(nums[i]);
    			temp[1] = i;
    		}else {
    			map.put(target - nums[i], i);
    		}
    	}
    	System.out.println("输出数组：temp = ["+temp[0]+","+temp[1]+"]");
    }
    public static void twoSum4(int[] nums, int target) {
        int[] result = new int[2];
        int[] copyNums = new int[nums.length];
        System.arraycopy(nums, 0, copyNums, 0, nums.length);
        Arrays.sort(nums);
        int sIndex = 0;
        int eIndex = nums.length - 1;
        for (int i = 0; i < nums.length; i++) {
            if (nums[sIndex] + nums[eIndex] == target) {
                result[0] = nums[sIndex];
                result[1] = nums[eIndex];
                break;
            } else if (nums[sIndex] + nums[eIndex] > target) {
                eIndex--;
            } else {
                sIndex++;
            }

        }

        boolean fGit = false;
        for (int i = 0; i < copyNums.length; i++) {
            if (!fGit && copyNums[i] == result[0]) {
                sIndex = i;
                fGit = true;
            } else if (copyNums[i] == result[1]) {
                eIndex = i;
            }
        }
        if (sIndex > eIndex) {
            result[0] = eIndex;
            result[1] = sIndex;
        } else {
            result[0] = sIndex;
            result[1] = eIndex;
        }

        System.out.println("输出数	组：temp = ["+result[0]+","+result[1]+"]");
    }
	public static void main(String[] args) {
		int[] a = {2, 7, 11, 15};
		twoSum(a,9);
	}

}