454. 四数相加 II - 力扣（Leetcode）

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

//四数相加II454

public class FourSumII454 {
	public static void main(String[] args) {
		int[] nums1 = {1,2}; 
		int[] nums2 = {-2,-1};
		int[] nums3 = {-1,2};
		int[] nums4 = {0,2};
		System.out.println(new Solution().fourSumCount(nums1,nums2,nums3,nums4));
	}
}

class Solution {
    public int fourSumCount(int[] nums1, int[] nums2, int[] nums3, int[] nums4) {
    	int res = 0;
    	Map<Integer,Integer> map = new HashMap<>();
    	//上两个
    	for (int num01 : nums1) {
    		for (int num02 : nums2 ) {
    			int sum01 = num01 + num02;
    			if (map.containsKey(sum01)) {
    				map.put(sum01,map.get(sum01) + 1);
    			}else{
    				map.put(sum01,1);
    			}
    		}
    	}
    	//下面两个
    	for (int num03 : nums3) {
    		for (int num04 : nums4 ) {
    			int needNum01 = 0 - (num03 + num04);
    			if (map.containsKey(needNum01)) {
    				res += map.get(needNum01);
    			}
    		}
    	}
    	return res;
    }
}