leetcode_hash 01. 两数之和 03. 无重复字符的最长子串

目录

 

01.  两数之和

03. longest-substring-without-repeating-characters  无重复字符的最长子串

---

 

01.  两数之和

两遍hash

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

 一遍hash

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

03. longest-substring-without-repeating-characters  无重复字符的最长子串

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        if(s.size() == 0) return 0;
        unordered_set<char> lookup; //hash表
        int maxStr = 0;
        int left = 0;
        for(int i = 0; i < s.size(); i++){
            while (lookup.find(s[i]) != lookup.end()){
                lookup.erase(s[left]);
                left ++;
            }
            maxStr = max(maxStr,i-left+1);
            lookup.insert(s[i]);
    }
        return maxStr;
        
    }
};

//c++

//java
class Solution {
    public int lengthOfLongestSubstring(String s) {
        if (s.length()==0) return 0;
        HashMap<Character, Integer> map = new HashMap<Character, Integer>();
        int max = 0;
        int left = 0;
        for(int i = 0; i < s.length(); i ++){
            if(map.containsKey(s.charAt(i))){
                left = Math.max(left,map.get(s.charAt(i)) + 1);
            }
            map.put(s.charAt(i),i);
            max = Math.max(max,i-left+1);
        }
        return max;
        
    }
}