1. 两数之和

  1.     public int[] twoSum(int[] nums, int target) {
  2.         int n = nums.length;
  3.         for (int i = 0; i < n; ++i) {
  4.             for (int j = i + 1; j < n; ++j) {
  5.                 if (nums[i] + nums[j] == target) {
  6.                     return new int[]{i, j};
  7.                 }
  8.             }
  9.         }
  10.         return new int[0];
  11.     }
  13.     public int[] twoSum2(int[] nums, int target) {
  14.         Map<Integer, Integer> hashtable = new HashMap<Integer, Integer>();
  15.         for (int i = 0; i < nums.length; ++i) {
  16.             if (hashtable.containsKey(target - nums[i])) {
  17.                 return new int[]{hashtable.get(target - nums[i]), i};
  18.             }
  19.             hashtable.put(nums[i], i);
  20.         }
  21.         return new int[0];
  22.     }
  25. //链接：https://leetcode-cn.com/problems/two-sum/solution/liang-shu-zhi-he-by-leetcode-solution/
  27. }