01.两数之和

给定 nums = [2, 7, 11, 15], target = 9
因为 nums[0] + nums[1] = 2 + 7 = 9
所以返回 [0, 1]

class Solution {
    public int[] twoSum(int[] nums, int target) {
        int[] arr = new int[2];
        for(int i=0;i<nums.length;i++){
            for(int j=(i+1);j<nums.length;j++){
                if(nums[i]+nums[j] == target){
                    arr[0] = i;
                    arr[1] = j;
                    return arr;
                }
            }
        }
        throw new IllegalArgumentException("No two sum solution");
    }
}

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