1. 两数之和

class Solution {
	HashMap<Integer, Integer>hm ;
	public int[] twoSum(int[] nums, int t) {
		int [] ans = new int[2] ;
		hm = new HashMap<Integer, Integer>();
		for(int i = 0 ; i < nums.length ; i++) {
            if(hm.containsKey(t-nums[i])) {
				ans[1] = i;
				ans[0] = hm.get(t-nums[i]);
			}
			hm.put(nums[i],i );
		}
		return ans;
	}
}

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

}