2025-12-25-力扣百题速练（Javascript/TypeScript）Vol.1

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function addTwoNumbers(l1: ListNode | null, l2: ListNode | null): ListNode | null {
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  const dummy: ListNode = new ListNode(0);
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  // 哑节点，没有 dummy，直接从第一个节点开始构建，结果链表的头节点会在循环中不断变化
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  //需要额外判断是否是第一个节点
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  let tail: ListNode = dummy;
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  //始终指向结果链表的“当前最后一个节点”。
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  //每次计算出一位新数字后，直接在 tail 后面添加新节点
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  let carry: number = 0;
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  // 进位，当前这一位加完后，是否需要给下一位（更高位）额外加 1
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  while (l1 !== null || l2 !== null || carry !== 0) {
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    const val1: number = l1 ? l1.val : 0;
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    const val2: number = l2 ? l2.val : 0;
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    const sum: number = val1 + val2 + carry;
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    const digit: number = sum % 10;
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    carry = Math.floor(sum / 10);
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    tail.next = new ListNode(digit);
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    tail = tail.next;
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    if (l1) l1 = l1.next;
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    if (l2) l2 = l2.next;
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  }
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  return dummy.next;
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}

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function lengthOfLongestSubstring(s: string): number {
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    const charSet = new Set<string>();  // 记录窗口内字符
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    let left = 0;                       // 左指针
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    let maxLength = 0;                  // 最大长度
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    for (let right = 0; right < s.length; right++) {
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        // 若当前字符已存在，收缩左指针
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        while (charSet.has(s[right])) {
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            charSet.delete(s[left]);
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            left++;
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        }
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        charSet.add(s[right]);
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        maxLength = Math.max(maxLength, right - left + 1);
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    }
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    return maxLength;
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}

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function reverse(x: number): number {
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  if (x === 0) {
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    return x;
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  }
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  const MAX = 2 ** 31 - 1;
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  const MIN = -(2 ** 31);
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  let mid = x.toString();
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  let LI: boolean = true;
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  if (mid[0] === "-") {
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    LI = false;
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  }
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  const reverseString = mid.split("").reverse().join("");
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  if (LI === true) {
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    if (parseInt(reverseString) < MIN || parseInt(reverseString) > MAX) {
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      return 0;
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    }
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    return parseInt(reverseString);
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  }
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  if (LI === false) {
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    let fin = reverseString.slice(0, reverseString.length - 1);
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    let fin2 = -parseInt(fin);
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    if (fin2 < MIN || fin2 > MAX) {
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      return 0;
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    }
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    return fin2;
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  }
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}

1
function myAtoi(s: string): number {
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  let max = 2 ** 31 - 1;
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  let min = -(2 ** 31);
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  let i: number = 0;
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  let sign: number = 1;
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  let fin = "";
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  let clac = 0;
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  if (i <= s.length) {
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    while (s[i] === " ") {
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      i++;
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    }
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    while (s[i] === "-" || s[i] === "+") {
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      if (s[i] === "-") {
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        sign = -1;
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      }
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      if (s[i] === "+") {
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        sign = 1;
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      }
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      if (clac === 1) {
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        return 0;
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      }
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      clac = 1;
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      i++;
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    }
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    while (s[i] <= "9" && s[i] >= "0") {
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      fin = fin + s[i];
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      i++;
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    }
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    if (fin === "") return 0;
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    if (sign === 1) {
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      if (parseInt(fin) >= max) {
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        return max;
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      }
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      if (parseInt(fin) <= min) {
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        return min;
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      }
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      return parseInt(fin);
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    }
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    if (sign === -1) {
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      if (-parseInt(fin) >= max) {
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        return max;
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      }
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      if (-parseInt(fin) <= min) {
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        return min;
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      }
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      return -fin;
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    }
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  }
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}

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function isMatch(s: string, p: string): boolean {
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  if (s == p) {
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    return true;
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  }
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  let sindex = 0;
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  let pindex = 0;
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  while (sindex < s.length && pindex < p.length) {
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    if (s[sindex] === p[pindex] || p[pindex] === ".") {
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      sindex++;
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      pindex++;
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    }
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    if (p[pindex] === "*") {
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      while (s[sindex] === s[sindex + 1]) {
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        sindex++;
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      }
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      pindex++;
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    }
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    if (s[sindex] !== p[pindex]) {
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      if (p[pindex] !== "*" && p[pindex] !== ".") {
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        return false;
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      }
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    }
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    return true;
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  }
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}

1
function isMatch(s: string, p: string): boolean {
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  const m = s.length,
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    n = p.length;
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  const dp = Array(m + 1)
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    .fill(null)
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    .map(() => Array(n + 1).fill(false));
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  dp[0][0] = true;
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  for (let j = 2; j <= n; j++) {
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    if (p[j - 1] === "*") {
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      dp[0][j] = dp[0][j - 2];
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    }
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  }
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  for (let i = 1; i <= m; i++) {
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    for (let j = 1; j <= n; j++) {
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      if (p[j - 1] === "*") {
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        dp[i][j] =
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          dp[i][j - 2] ||
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          ((s[i - 1] === p[j - 2] || p[j - 2] === ".") && dp[i - 1][j]);
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      } else {
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        dp[i][j] =
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          (s[i - 1] === p[j - 1] || p[j - 1] === ".") && dp[i - 1][j - 1];
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      }
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    }
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  }
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  return dp[m][n];
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}