leetcode two-sum

题目

给一个数组和一个和，查找出数组中两个数相加为给定的和

Given an array of integers, return indices of the two numbers such that they add up to a specific target.

two-sum

public class TwoSum {

    public static void main(String[] args) {
        int[] nums = { 1, 3, 4, 5, 6 };
        int[] result = twoSum(nums, 10);
        System.out.println("result[0]:" + result[0] + ", result[1]=" + result[1]);
        
        result = twoSum2(nums, 10);
        System.out.println("result[0]:" + result[0] + ", result[1]=" + result[1]);
    }

    public static int[] twoSum(int[] nums, int target) {
        Map<Integer, Integer> map = new HashMap<>();
        int length = nums.length;
        for (int i = 0; i < length; i++) {
            map.put(nums[i], i);
        }

        for (int i = 0; i < 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");
    }
    
    public static int[] twoSum2(int[] nums, int target) {
        Map<Integer, Integer> map = new HashMap();
        int length = nums.length;
        for(int i = 0; i < length; i++){
            int complement = target - nums[i]; 
            if(map.containsKey(complement) && map.get(complement) != i){
                return new int[]{i, map.get(complement)};
            }
            map.put(nums[i], i);
        }
        throw new IllegalArgumentException("No two sum solution");
    }

}