public class Solution {
    public int[] twoSum(int[] numbers, int target) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(numbers==null) return null;
        
        int[] now = new int[numbers.length];
        System.arraycopy(numbers,0,now,0,numbers.length);
        Arrays.sort(numbers);
        int i = 0,j=numbers.length-1;
        
        while(i<j){
            if(numbers[i]+numbers[j]>target){
                j--;
            }else if(numbers[i]+numbers[j]<target){
                i++;
            }else{
                int x =0;
                for(x=0;x<now.length;x++){
                    if(now[x]==numbers[i])
                    break;
                }
                //注意題目希望返回下標(biāo)，所以要留意重新排序后造成的下標(biāo)變化問題
                int y=0;
                for(y=0;y<now.length;y++){
                    if(x!=y && now[y]==numbers[j])
                    break;
                }
                /*
                if(now[x]<now[y]){
                    int temp = x;
                    x=y;
                    y=temp;
                }*/
                
                int [] res = new int[2];
                res[0]=x+1;
                res[1]=y+1;
                Arrays.sort(res);   //返回的下標(biāo)是要有序的！
                return res;
            }
            
        }
          return null;
        
    }
}

Line 16: ']' expected

Line 24: missing return statement

 
 

  
  Last executed input
 
 
[5,75,25], 100

Showing the first failed test case.

 
 
input
output
expected
?
[5,75,25],
 100
1, 2
2, 3

     
     

      
      ? 
     
     

Showing the first failed test case.

 
 
input
output
expected
?
[150,24,79,50,88,345,3],
 200
3, 6
1, 4

     
     

      
      ? 
     
     

Line 7: incompatible types

Line 8: cannot find symbol: method copy(int[],int[])

Line 8: cannot find symbol: method copyOf(int[],int[])

Line 29: cannot find symbol: variable x

Showing the first failed test case.

 
 
input
output
expected
?
[5,75,25],
 100
3, 2
2, 3

     
     

      
      ? 
     
     

Showing the first failed test case.

 
 
input
output
expected
?
[5,75,25],
 100
3, 2
2, 3

     
     

      
      ? 
     
     

Showing the first failed test case.

 
 
input
output
expected
?
[5,75,25],
 100
3, 2
2, 3

     
     

      
      ? 
     
     

Showing the first failed test case.

 
 
input
output
expected
?
[2,1,9,4,4,56,90,3],
 8
4, 4
4, 5

     
     

      
      ? 
     
     

Showing the first failed test case.

 
 
input
output
expected
?
[230,863,916,585,981,404,316,785,88,12,70,435,384,778,887,755,740,337,86,92,325,422,815,650,920,125,277,336,221,847,168,23,677,61,400,136,874,363,394,199,863,997,794,587,124,321,212,957,7,173,314,422,927,783,930,282,306,506,44,926,691,568,68,730,933,737,531,180,414,751,28,6,60,371,493,370,527,387,43,1,13,457,328,227,652,365,430,803,59,858,538,427,583,368,375,173,809,6,370,7],
 2
46, 29
29, 46

     
     

      
      ? 
     
     

    For example, given array S = {-1 0 1 2 -1 -4},

    A solution set is:
    (-1, 0, 1)
    (-1, -1, 2)

public class Solution {
    public static ArrayList<ArrayList<Integer>> threeSum(int[] num) {
		// Start typing your Java solution below
		// DO NOT write main() function
		if (num == null)
			return null;


		ArrayList<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();
		Arrays.sort(num);
		for (int i = 0; i < num.length-2; i++) {
			if (i > 0 && num[i] == num[i - 1])  continue;




			int j = i + 1, k = num.length - 1;
			while (j < k) {
				if (num[j] + num[k] > -num[i]) {
					k--;
				} else if (num[j] + num[k] < -num[i]) {
					j++; // 寫錯(cuò)成i了....
				} else {
					ArrayList<Integer> a = new ArrayList<Integer>();
					a.add(num[i]);  //放的不是ijk 而是他們的值！
					a.add(num[j]); 
					a.add(num[k]);
					list.add(a);
                    j++;  //這些步驟是為了排除掉 j k里面存在重復(fù)的地方！
                    k--;   
                    while(j<k && num[j]==num[j-1]) j++;
                    while(j<k && num[k]==num[k+1])  k--;
				}
			}
			
		}
		return list;
	}
}

Line 27: illegal start of type

Showing the first failed test case.

 
 
input
output
expected
?
[]
null
[]

     
     

      
      ? 
     
     

Showing the first failed test case.

 
 
input
output
expected
?
[0,0,0]
[]
[[0,0,0]]

     
     

      
      ? 
     
     

Showing the first failed test case.

 
 
input
output
expected
?
[0,0,0]
[[0,1,2]]
[[0,0,0]]

     
     

      
      ? 
     
     

    For example, given array S = {-1 2 1 -4}, and target = 1.

    The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

public class Solution {
    public int threeSumClosest(int[] num, int target) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(num==null) return -1;
        
        int goal = 0;  //不設(shè)為最大值！ 因?yàn)榧蛹訙p減會(huì)造成溢出！
        boolean ifinit = false; //加入變量，來讓goal有個(gè)初值！
        
        Arrays.sort(num);
        for(int i=0;i<num.length-2;i++){
         if(i>0 && num[i]==num[i-1]) continue;
         int j= i+1,k=num.length-1;
         
         while(j<k){
             int now = num[i]+num[j]+num[k];
             if(!ifinit||Math.abs(now-target)<Math.abs(goal-target) ){ 
                 goal = now;
                 ifinit = true;
             }
             if(now>target){
                 k--;
                    while(j<k && num[k]==num[k+1]) k--;  //前提條件！??！
             }else{
                 j++;
                   while(j<k && num[j]==num[j-1]) j++;
             }
           
         }
        }
        return goal;
    }
}

Line 16: ')' expected

 
 

  
  Last executed input
 
 
[0,0,0], 1

Showing the first failed test case.

 
 
input
output
expected
?
[1,1,-1,-1,3],
 -1
21474837
-1

     
     

      
      ? 
     
     

Line 17: cannot find symbol: variable init

Line 17: variable goal might not have been initialized

? 4sum ?大數(shù)據(jù)超時(shí) ?時(shí)間復(fù)雜度 n*3

 public static ArrayList<ArrayList<Integer>> fourSum(int[] num, int target) {
	        if(num==null) return null;
	        
	        Arrays.sort(num);
	        ArrayList<ArrayList<Integer>>  list = new ArrayList<ArrayList<Integer>> ();
	        
	        for(int i=0;i<num.length-3;i++){
	            if(i>0 && num[i]==num[i-1])  continue;
	            
	            for(int j=i+1;j<num.length-2;j++){
	                if(j>i+1 && num[j]==num[j-1]) continue;  //這里請(qǐng)注意j是從i+1開始的?。?！
	                
	                int k = j+1,m = num.length-1;
	                while(k<m){
	                    if(num[i]+num[j]+num[k]+num[m]==target){
	                        ArrayList<Integer> a = new ArrayList<Integer>();
	                        a.add(num[i]);
	                        a.add(num[j]);
	                        a.add(num[k]);
	                        a.add(num[m]);
	                        list.add(a);
	                        k++;
	                        m--;
	                        while(k<m && num[k]==num[k-1]) k++;
	                        while(k<m && num[m]==num[m+1]) m--;
	                    }else if(num[i]+num[j]+num[k]+num[m]>target){
	                        m--;
	                    }else{
	                        k++;
	                    }
	                }
	            }
	        }
	        return list;
	    }