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【刷题记录】1. 两数之和
2022-07-05 20:21:00 【InfoQ】
前言
一、题目描述
输入:nums = [2,7,11,15], target = 9
输出:[0,1]
解释:因为 nums[0] + nums[1] == 9 ,返回 [0, 1] 。
输入: nums = [3,2,4], target = 6
输出: [1,2]
1 <= s.length <= 1000
s
由英文字母(小写和大写)、','
和 '.'
组成
1 <= numRows <= 1000
二、思路分析:
1.简单直接暴力解法 - 遍历
class Solution {
public int[] twoSum(int[] nums, int target) {
int length = nums.length;
//保证num[j]存在 i 遍历到 n-2 为止
for (int i = 0; i < length - 1; i++) {
//避免重复,遍历从当前数组后面开始
for (int j = i + 1; j < length; j++) {
if (nums[i] + nums[j] == target) return new int[]{i,j};
}
}
return new int[]{};
}
}
2.改进下解法-哈希表
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(target - nums[i])) return new int[]{map.get(target - nums[i]), i};
map.put(nums[i], i);
}
return new int[]{};
}
}
总结
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