题解 | #三数之和#
三数之和
https://www.nowcoder.com/practice/345e2ed5f81d4017bbb8cc6055b0b711
思路:别想着取巧,老老实实做三层循环
import java.util.*; public class Solution { public ArrayList<ArrayList<Integer>> threeSum(int[] num) { ArrayList<ArrayList<Integer>> out = new ArrayList<>(); if (num.length < 3) { return out; } else { for (int i = 0; i < num.length; i++) {//第一层循环,逐个取出数字 int sumtwo = 0 - num[i]; //第二层循环,找到满足条件的(即和为0-num[i])其他两个数字 for (int j = i+1; j < num.length; j++) { int one = sumtwo - num[j]; //第三层循环,找到跟num[j]的和为0-num[i]的数字,从j右边的数字开始 for (int k = j + 1; k < num.length; k++) { ArrayList<Integer> out0 = new ArrayList<>(); if (num[k] == one) {//找到满足条件的数字,排序后加入out并去重 out0.add(num[i]); out0.add(num[j]); out0.add(num[k]); out0.sort(Comparator.comparingInt(s->s)); if (!out.contains(out0)){out.add(new ArrayList<>(out0));} break; } } } } //out排序,按三元组中第一个数字升序排列,若第一个数字相等则按第二个,若第一第二相等则按第三个 out.sort((c, f)-> { if (c.get(0) > f.get(0)) { return 1; } else if (c.get(0) == f.get(0) && c.get(1) > f.get(1)) { return 1; } else if (c.get(0) == f.get(0) && c.get(1) == f.get(1) && c.get(2) > f.get(2)) { return 1; } else { return -1; } }); return out; } } }