packagemedium;

importjava.util.Arrays;

importjava.util.HashMap;

importjava.util.Map;

publicclass_4SumII {

publicstaticintfourSumCount(int[]A,int[]B,int[]C,int[]D) {

Map<Integer,Integer>map =newHashMap();

intresult =0,len =A.length;

for (inti =0;i <len;i++){

for (intj =0;j <len;j++){

intsum =A[i] +B[j];

if (map.containsKey(sum)){

map.put(sum,map.get(sum)+1);

}else {

map.put(sum,1);

}

}

}

for (inti =0;i <len;i++){

for (intj =0;j <len;j++){

intsum = -(C[i] +D[j]);

if(map.containsKey(sum))result +=map.get(sum);

}

}

returnresult;

}

publicstaticvoidmain(String...args){

int[]A =newint[]{1,2};

int[]B =newint[]{-2,-1};

int[]C =newint[]{-1,2};

int[]D =newint[]{0,2};

System.out.println(fourSumCount(A,B,C,D));

}

}

|459|[Repeated Substring Pattern](https://leetcode.com/problems/repeated-substring-pattern/)|[Solution](../../blob/master/EASY/src/easy/RepeatedSubstringPattern.java)| O(n)|O(n) | Easy| KMP

|456|[132 Pattern](https://leetcode.com/problems/132-pattern/)|[Solution](../../blob/master/MEDIUM/src/medium/_132Pattern.java) | O(n) |O(n) | Medium| Stack

|455|[Assign Cookies](https://leetcode.com/problems/assign-cookies/)|[Solution](../../blob/master/EASY/src/easy/AssignCookies.java)| O(n)|O(1)| Easy|

|454|[4Sum II](https://leetcode.com/problems/4sum-ii/)|[Solution](../../blob/master/MEDIUM/src/medium/_4SumII.java) | O(n) |O(n) | Medium| HashMap

|453|[Minimum Moves to Equal Array Elements](https://leetcode.com/problems/minimum-moves-to-equal-array-elements/)|[Solution](../../blob/master/EASY/src/easy/MinimumMovestoEqualArrayElements.java)| O(n)|O(1)| Easy|

|447|[Number of Boomerangs](https://leetcode.com/problems/number-of-boomerangs/)|[Solution](../../blob/master/EASY/src/easy/NumberofBoomerangs.java)| O(n^2)|O(n) | Easy| HashMap

|441|[Arranging Coins](https://leetcode.com/problems/arrange-coins/)|[Solution](../../blob/master/EASY/src/easy/ArrangingCoins.java)| O(n)|O(1)| Easy|