三数和为k

两数和为k

给定一个数组,试找出2个数a, b,使得a+b=k

import java.util.*;
public class task1 {
    public static void main(String[] args){
        int[] arr = new int[]{1,2,3,88,5,7,9,11,45,12,8,10,13,15,19,21,25,27};
        Arrays.sort(arr);
        int k = 11;
        sumAB(arr,k);
    }
    public static void sumAB(int[] arr,int k){
        int l=0,r=arr.length-1;
        while(l < r){
            int a = arr[l];
            int b = arr[r];
            if(a + b == k){
                int[] res = new int[]{a,b};
                System.out.println(Arrays.toString(res));
                l++;
                --r;
            }else if(a + b < k){
                ++l;
            }else{
                --r;
            }
        }
    }
}

三数和为k

给定一个数组,试找出3个数a, b, c,使得a+b+c=k

class Solution {
    public List<List<Integer>> threeSum(int[] nums) {
        List<List<Integer>> res = new ArrayList<>();
        Arrays.sort(nums);
        threeSumCore(nums,res);
        return res;
    }
    private void threeSumCore(int[] nums,List<List<Integer>> res){
        int n = nums.length;
        for(int i = 0; i < n - 2; ++i){
            //避免1，1，2，3情况
            if(i>0 && nums[i] == nums[i-1]){
                continue;
            }
            int l = i + 1;
            int r = n - 1;
            while(l < r){
                int temp = nums[i] + nums[l] + nums[r];
                if(temp == 0){
                    List<Integer> list = new ArrayList<>();
                    list.add(nums[i]);
                    list.add(nums[l]);
                    list.add(nums[r]);
                    res.add(list);
                    //避免0，0，0情况
                    while(l < r && nums[l] == nums[l + 1])++l;
                    while(l < r && nums[r] == nums[r - 1])--r;
                    ++l;
                    --r;
                }else if(temp < 0){
                    ++l;
                }else{
                    --r;
                }
            }
        }
    }
}