LeetCode Hot100 - 环形链表

142. 环形链表 II（见LeetCode Hot100 链表、LeetCode Hot100 双指针）

var detectCycle = function(head) {
    if(!head) return null
    let fast = head
    let slow = head
    while(fast?.next?.next) {
        fast = fast.next.next
        slow = slow.next
        if(fast === slow) {
            let res = head
            while(res !== slow) {
                res = res.next
                slow = slow.next
            }
            return res
        }
    }
 
    return null
};

141. 环形链表（见LeetCode Hot100 链表、LeetCode Hot100 双指针、JavaScript 算法基础第二天）

var hasCycle = function(head) {
    let fast = head
    let slow = head
    while(fast?.next?.next) {
        fast = fast.next.next
        slow = slow.next
        if(fast ===slow) {
            return true
        }
    }
    return false
};

139. 单词拆分（见LeetCode Hot100 hash表）

var wordBreak = function(s, wordDict) {
    const set = new Set(wordDict)
    const len = s.length
    const dp = Array.from({length: len + 1}).fill(false)
    dp[0] = true
    for(let i= 1; i<= len; i++) {
        for(let j = 0;j < i;j++) {
            if(dp[j] && set.has(s.slice(j, i))){
                dp[i] = true
                break
            }
        }
    }
    return dp[len]
 
};

136. 只出现一次的数字

var singleNumber = function(nums) {
    let res = 0
    for(let x of nums) {
        res ^=x
    }
    return res
};

647. 回文子串（见LeetCode Hot100 双指针）

var countSubstrings = function(s) {
    if(!s.length) return 0
    let res= 0
 
    const extend = (l, r) => {
        while(l>=0 && r < s.length && s[l] == s[r]){
            l--
            r++
            res++
        }
    }
 
    for(let num = 0; num < s.length; num++) {
        extend(num, num)
        extend(num, num+1)
    }
 
    return res
};

128. 最长连续序列（见LeetCode Hot100 hash表）

var longestConsecutive = function(nums) {
    const set = new Set(nums)
    let long = 0
 
    for (let num of set) {
        if(!set.has(num-1)) {
            currLong = 1
            n = 1
            while(set.has(num+n)) {
                currLong++
                n++
            }
            long = Math.max(long, currLong)
        }
    }
    return long
};

相关笔记

• 链表基础
• LeetCode Hot100 链表
• LeetCode Hot100 双指针