toSum

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]
 
java代码：

 public class Solution {
     public int[] twoSum(int[] nums, int target) {
         for(int i=0;i<nums.length;i++){
             for(int j=1;j<nums.length;j++){
                 if(target==nums[i]+nums[j]){
                     return new int[]{i,j};
                 }
             }
         }
         throw new RuntimeException("No such this indices");
     }
 }

 public class Solution {
    public int[] twoSum(int[] numbers, int target) {
     int[] result = new int[2];
     Map<Integer, Integer> map = new HashMap<Integer, Integer>();
     for (int i = 0; i < numbers.length; i++) {
         if (map.containsKey(target - numbers[i])) {
             result[1] = i;
             result[0] = map.get(target - numbers[i]);
             return result;
         }
         map.put(numbers[i], i + 1);
     }
     return result;
 }
 }

 public int[] twoSum(int[] nums, int target) {
     Map<Integer, Integer> map = new HashMap<>();
     for (int i = 0; i < nums.length; i++) {
         map.put(nums[i], i);
     }
     for (int i = 0; i < nums.length; i++) {
         int complement = target - nums[i];
         if (map.containsKey(complement) && map.get(complement) != i) {
             return new int[] { i, map.get(complement) };
         }
     }
     throw new IllegalArgumentException("No two sum solution");
 }