【leetcode】_3Sum

• 外加一层循环，遍历数组所有数，作为第一个数，其他两个与2sum类似，a+b=target结束循环，如果小就a+，如果大就b-
• 将满足条件的结果（三个数字）放入midresult中，midresult是个链表，将midresult放入hashmap中去重
• 再将hashmap中取出来放入result中即可

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public class _3Sum {

public static ArrayList threeSum(int[] num) {

Arrays.sort(num);

ArrayList result = new ArrayList();

Map hm = new HashMap();

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for (int firstPos = 0; firstPos < num.length; firstPos++) {

int secPos = firstPos + 1;

int thirdPos = num.length - 1;

while (secPos < thirdPos) {

if (num[firstPos] + num[secPos] + num[thirdPos] == 0) {

ArrayList<Integer> midResult = new ArrayList<Integer>();

midResult.add(num[firstPos]);

midResult.add(num[secPos]);

midResult.add(num[thirdPos]);

hm.put(midResult, false);

secPos += 1;

thirdPos -= 1;

} else if (num[firstPos] + num[secPos] + num[thirdPos] < 0) {

secPos += 1;

} else {

thirdPos -= 1;

}

}

}

Iterator it = hm.entrySet().iterator();

while (it.hasNext()) {

//????????????????????????Entry entry =(Entry) it.next();

//????????????????????????result.add(entry.getKey());

result.add(it.next());

}

return result;

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}

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public static void main(String[] args) {

//????????????????int[] num = { -1, 0, 1, 2, -1, -4,-1,0,1};

int[] num = {0,0,0};

System.out.println(threeSum(num));

}

}