算法练习-001-返回目标数的下标组合

 question:

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Given an array of integers, return indices of the two numbers such that they add up to a specific target.   You may assume that each input would have exactly one solution, and you may not use the same element twice.   Example:   Given nums = [2, 7, 11, 15], target = 9,   Because nums[0] + nums[1] = 2 + 7 = 9, return [0, 1].

　

my solution

class Solution {
    public int[] twoSum(int[] nums, int target) {
         int [] result = new int[2] ;
     for (int i = 0; i < nums.length-1; i++) {
            for (int j = i+1; j < nums.length; j++) {
                if(nums[i]+nums[j] == target){
                    result[0]=i;
                    result[1]=j;
                    //System.out.println("elem1:"+i+";elem2:"+j);
                }
        } 
    }
        return result;
        
    }
}

 

 

 

 

 

 

7ms的comminter code

class Solution {
    public int[] twoSum(int[] nums, int target) {
        int m = 0;
        Map<Integer, Integer> map = new HashMap<Integer, Integer>();
         for (int i=0; i < nums.length; i++){
             map.put(nums[i], i);
         }
        for(int j=0; j<nums.length; j++){
            m = target - nums[j];
            if (map.containsKey(m)&&(map.get(m)!=j))
                return new int[] {j, map.get(m)};
        }
        throw new IllegalArgumentException("No two sum solution");
    }
    
}

 

 

 

 

 

 

5ms的comminter code

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class Solution {     public int[] twoSum(int[] nums, int target) {         if(nums == null) return new int[0];         HashMap<Integer, Integer> map = new HashMap<>();         for(int i=0; i<nums.length; i++){             int complement = target - nums[i];             if(map.containsKey(complement)){                 return new int[]{i,map.get(complement)};             }             else map.put(nums[i], i);         }         return new int[0];     } }

　　

 

 

4ms的comminter code

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class Solution {     public int[] twoSum(int[] nums, int target) {         int len=nums.length;         HashMap<Integer, Integer> map=new HashMap<>();         map.put(nums[0], 0);         for(int i=1;i<len;i++){             if(map.containsKey(target-nums[i])){                 int[] returnArray={map.get(target-nums[i]),i};                 return returnArray;             } else{                 map.put(nums[i], i);             }         }         int[] returnArray={0,0};         return returnArray;     } }

 

3ms的comminter code

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class Solution {     public int[] twoSum(int[] nums, int target) {         int[] res = new int[]{-1, -1};         if (nums == null || nums.length < 2) return res;         int n = nums.length;         int left = 0;         int right = n - 1;         for(int i = 0; i < n; i++) {             nums[i] = nums[i] * n + (nums[i] < 0 ? -i : i);         }         Arrays.sort(nums);           while (left < right) {             int sum = nums[left] / n + nums[right] / n;             if (sum == target) {                 res[0] = nums[left] < 0 ? -nums[left] % n : nums[left] % n;                 res[1] = nums[right] < 0 ? -nums[right] % n : nums[right] % n;                 return res;             } else if (sum < target) {                 left++;             } else {                 right--;             }         }         throw new IllegalArgumentException();     } }

　　

 

 

 

2ms的comminter code

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class Solution {     public int[] twoSum(int[] nums, int target) {     int max = 2048;     int[] indexes = new int[max];     int bitMode = --max;     int first = nums[0];       for (int i = 1; i < nums.length; i++) {       int difference = target - nums[i];       if (difference == first) {         return new int[]{0, i};       }       int index = indexes[difference&bitMode];       if(index != 0) {         return new int[]{index, i};       }       indexes[nums[i]&bitMode] = i;     }     return new int[0];   } }