leetcode-two sum

package test1;

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


public class TwoSum {

    public static void main(String[] args) {
        int[] arr = {1, 3, 5, 8, 9};
        System.out.println("-------------暴力法-------------");
        printArray(bruteForce(arr, 12));
        System.out.println("-------------暴力法-------------");

        System.out.println("-------------两步哈希表-------------");
        printArray(twoStepHashTable(arr, 12));
        System.out.println("-------------两步哈希表-------------");

        System.out.println("-------------一步哈希表-------------");
        printArray(oneStepHashTable(arr, 12));
        System.out.println("-------------一步哈希表-------------");
    }

    private static int[] oneStepHashTable(int[] nums, int target) {
        Map map = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            if (map.get(target - nums[i]) != null) {
                return new int[]{map.get(target - nums[i]), i};
            }
            map.put(nums[i], i);
        }
        return null;
    }

    
    private static int[] twoStepHashTable(int[] nums, int target) {
        Map map = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            map.put(nums[i], i);
        }
        for (Map.Entry entry : map.entrySet()) {
            if (map.get(target - entry.getKey()) != null) {
                return new int[]{entry.getValue(), map.get(target - entry.getKey())};
            }
        }
        return null;
    }

    
    public static int[] bruteForce(int[] nums, int target) {
        for (int i = 0; i < nums.length; i++) {
            int result = target - nums[i];
            for (int j = i + 1; j < nums.length; j++) {
                if (nums[j] == result) {
                    return new int[]{i, j};
                }
            }
        }
        return null;
    }

    
    private static void printArray(int[] arr) {
        if (arr == null || arr.length == 0) {
            return;
        }
        for (int num : arr) {
            System.out.print(num + ",");
        }
        System.out.println();
    }
}