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.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,

return [0, 1].

public class Solution {

public int[] twoSum(int[] nums, int target) {

int[] result = new int[2];

if(nums.length == 0 || nums.length == 1) {

return result;

}

for (int i = 0; i < nums.length-1; i++) {

// if(nums[i] > target) {

// continue;

// }

for (int j = i + 1; j < nums.length; j++) {

// if(nums[j] > target) {

// continue;

// }

if(nums[i] + nums[j] == target) {

result[0] = i;

result[1] = j;

return result;

}

}

}

return result;

}

}

my second solution:

public class Solution {

public int[] twoSum(int[] nums, int target) {

Map<Integer, Integer> map = new HashMap<>();

int[] ans = new int[2];

for (int i = 0; i < nums.length; i++) {

if (map.get(target-nums[i]) != null) {

ans[0] = i;

ans[1] = map.get(target-nums[i]);

return ans;

}

map.put(nums[i],i);

}

return ans;

}

}

Tips:

1. no need to consider whethe a[i] > target, the numbers may be < 0; -1 -2