TwoSum.java

import java.util.HashMap;
import java.util.Map;

/**
 * 1. Two Sum
 * @author LBW
 */
public class TwoSum {
    /*
    方法一，暴力求解
     */
    public int[] twoSum(int[] nums, int target) {
        int length = nums.length;
        for (int i = 0; i < length; i++) {
            for (int j = i+1; j < length; j++) {
                if (nums[i] + nums[j] == target) {
                    return new int[]{i,j};
                }
            }
        }
        return new int[]{-1,-1};
    }

    /*
    方法二，哈希
     */
    public int[] twoSumTwo(int[] nums, int target) {
        Map<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            if (map.containsKey(target - nums[i])) {
                return new int[]{map.get(target - nums[i]), i};
            }
            map.put(nums[i], i);
        }
        return null;
    }
}