LeetCode 1. Two Sum

JAVA

① 暴力

class Solution {
    public int[] twoSum(int[] nums, int target) {
        int[] ans = new int[2];								//必须要固定数组个数
        for (int i = 0; i < nums.length - 1; i++) {
            for (int j = i + 1; j < nums.length; j++) {
                if (nums[i] + nums[j] == target) {
                    ans[0] = i;
                    ans[1] = j;
                    return ans;
                }
            }
        }
        return ans;											//否则打印 [0, 0] (初始化值)
    }
}

② 排序+双指针

import java.util.Arrays;

class Solution {
    public int[] twoSum(int[] nums, int target) {
        int n = 0, m = 0;									//JAVA的变量必须要初始化
        int[] ans = new int[2];
        int[] tmp = new int[nums.length];
        System.arraycopy(nums, 0, tmp, 0, nums.length);		//数组整体的复制 (前提是个数相同)
        Arrays.sort(nums);									//排序
        for (int i = 0, j = nums.length - 1; i < nums.length - 1; ) {
            if (nums[i] + nums[j] == target) {
                n = i;
                m = j;
                break;
            } else if (nums[i] + nums[j] < target) i++;
            else j--;
        }
        int i = 0;
        for (i = 0; i < nums.length; i++) {
            if (tmp[i] == nums[n]) {
                ans[0] = i;
                break;
            }
        }
        for (int k = 0; k < nums.length; k++) {
            if (tmp[k] == nums[m] && i != k) {				
                ans[1] = k;
                break;
            }
        }
        return ans;
    }
}

③ 哈希

import java.util.Arrays;
import java.util.HashMap;

class Solution {
    public int[] twoSum(int[] nums, int target) {
        HashMap<Integer, Integer> map = new HashMap<>();	//怪异的写法，JAVA的 STL
        for (int i = 0; i < nums.length; i++) {
            if(map.containsKey(target-nums[i])) {			//判断是否存在
                return new int[] {map.get(target-nums[i]),i};//直接输出数组的写法
            }
            map.put(nums[i],i);								//map的存入
        }
        return new int[] {-1,-1};
    }
}

Python

① 暴力

# from typing import List												# 测试代码时加上的库


class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:		# 返回值是整型数组
        for i in range(len(nums)):
            for j in range(i+1, len(nums)):
                if nums[i]+nums[j] == target:
                    return [i, j]
        return []


'''
List = [2, 7, 11, 15]
target = 9
so = Solution()
print(so.twoSum(List, target))
'''

② 排序+双指针

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        temp = nums.copy()											# 简便的数组复制方法
        temp.sort()
        i = 0
        j = len(nums)-1
        while i < j:
            if (temp[i]+temp[j]) > target:
                j = j-1
            elif (temp[i]+temp[j]) < target:
                i = i+1
            else:
                break
        p = nums.index(temp[i])										# 查找第一个下标
        nums.pop(p)													# 弹出 避免重复
        k = nums.index(temp[j])										# 因为弹出了 所以要加一
        if k >= p:
            k = k+1
        return [p, k]

③ 哈希

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        hashset = {}										# 创建字典
        for i in range(len(nums)):
            if hashset.get(target-nums[i]) is not None:		# 获取字典中目标键的值
                return [hashset.get(target-nums[i]), i]
            hashset[nums[i]] = i

python字典的用法