程序员面试金典（第 6 版）

• 面试题 01.01. 判定字符是否唯一
• 面试题 01.02. 判定是否互为字符重排
• 面试题 01.03. URL化
• 面试题 01.04. 回文排列
• 面试题 01.05. 一次编辑🔐
• 面试题 01.06. 字符串压缩🔐
• 面试题 01.07. 旋转矩阵
• 面试题 01.08. 零矩阵
• 面试题 01.09. 字符串轮转
• 面试题 02.01. 移除重复节点

面试题 01.01. 判定字符是否唯一

class Solution {
    public boolean isUnique(String astr) {
        if (astr == null || astr.length() <= 1) return true;
        boolean[] map = new boolean[26];
        for (char ch : astr.toCharArray()) {
            if (map[ch - 'a']) return false;
            map[ch - 'a'] = true;
        }
        return true;
    }
}

面试题 01.02. 判定是否互为字符重排

class Solution {
    public boolean CheckPermutation(String s1, String s2) {
        if (s1 == null && s2 == null) return true;
        if (s1 == null || s2 == null || s1.length() != s2.length()) return false;
        int[] map = new int[26];
        for (char ch : s1.toCharArray()) {
            ++map[ch - 'a'];
        }
        for (char ch : s2.toCharArray()) {
            if (map[ch - 'a'] == 0) return false;
            --map[ch - 'a'];
        }
        return true;
    }
}

面试题 01.03. URL化

class Solution {
    public String replaceSpaces(String S, int length) {
        if (S == null || S.length() == 0) return S;
        int num = 0;
        for (int i = 0; i < length; i++) {
            if (S.charAt(i) == ' ') {
                num++;
            }
        }
        char[] arr = new char[length + num * 2];
        int last = arr.length - 1, pre = length - 1;
        while (last >= 0) {
            if (S.charAt(pre) != ' ') arr[last--] = S.charAt(pre--);
            else {
                arr[last--] = '0';
                arr[last--] = '2';
                arr[last--] = '%';
                --pre;
            }
        }
        return new String(arr);
    }
}

面试题 01.04. 回文排列

class Solution {
    public boolean canPermutePalindrome(String s) {
        if (s == null || s.length() <= 1) return true;
        boolean[] map = new boolean[256];
        for (char ch : s.toCharArray()) {
            map[ch] ^= true;
        }
        boolean flag = false;
        for (boolean b : map) {
            if (b) {
                if (flag) return false;
                flag = true;
            }
        }
        return true;
    }
}

面试题 01.05. 一次编辑🔐

• oneEditAway(“teacher”,“lbeacher”)

class Solution {
    public boolean oneEditAway(String first, String second) {
        if (first.length() == 0 || second.length() == 0) return true;
        int subLen = first.length() - second.length();
        if (Math.abs(subLen) > 1) return false;
        int i = first.length() - 1, j = second.length() - 1;
        boolean flag = false;
        while (i >= 0 && j >= 0) {
            if (first.charAt(i) != second.charAt(j)) {
                if (subLen == -1) i++;// 阻止first-1
                else if (subLen == 1) j++;// 阻止second-1
                if (flag) return false;
                flag = true;
            }
            i--;
            j--;
        }
        return true;
    }
}

面试题 01.06. 字符串压缩🔐

class Solution {
    public String compressString(String S) {
        if (S == null || S.length() <= 1) return S;
        StringBuffer res = new StringBuffer();
        char[] arr = S.toCharArray();
        int pre = 0, N = arr.length;
        for (int i = 1; i < N; i++) {
            if (arr[i] != arr[i - 1]) {
                res.append(arr[i - 1]);
                res.append(i - pre);
                pre = i;
            }
        }
        res.append(arr[N - 1]);
        res.append(N - pre);
        return res.length() >= N ? S : res.toString();
    }
}

面试题 01.07. 旋转矩阵

class Solution {
    public void rotate(int[][] matrix) {
        if (matrix.length <= 1) return;
        int firstRow = 0, firstLine = 0, secondRow = matrix.length - 1, secondLine = matrix[0].length - 1;
        while (firstLine < secondLine && firstRow < secondRow) {
            circleSway(matrix, firstRow++, firstLine++, secondRow--, secondLine--);
        }
        for (int[] a : matrix) System.out.println(Arrays.toString(a));
    }

    private void circleSway(int[][] matrix, int locR1, int locL1, int locR2, int locL2) {
        for (int i = 0; i < locL2 - locL1; i++) {
            int temp = matrix[locR1][locL1 + i];
            matrix[locR1][locL1 + i] = matrix[locR2 - i][locL1];
            matrix[locR2 - i][locL1] = matrix[locR2][locL2 - i];
            matrix[locR2][locL2 - i] = matrix[locR1 + i][locL2];
            matrix[locR1 + i][locL2] = temp;
        }
    }
}

面试题 01.08. 零矩阵

class Solution {
    public void setZeroes(int[][] matrix) {
        if (matrix == null) return;
        int M = matrix.length, N = matrix[0].length;
        boolean[] rows = new boolean[M], lines = new boolean[N];
        for (int i = 0; i < M; i++) {
            for (int j = 0; j < N; j++) {
                if (matrix[i][j] == 0) {
                    rows[i] = true;
                    lines[j] = true;
                }
            }
        }
        for (int i = 0; i < M; i++) {
            for (int j = 0; j < N; j++) {
                if (rows[i] || lines[j]) {
                    matrix[i][j] = 0;
                }
            }
        }
    }
}

面试题 01.09. 字符串轮转

class Solution {
    public boolean isFlipedString(String s1, String s2) {
        if (s1 == null && s2 == null) return true;
        if (s1 == null || s2 == null) return false;
        if (s1.length() != s2.length()) return false;
        String s = s1 + s1;
        return s.contains(s2);
    }
}

面试题 02.01. 移除重复节点

class Solution {
    public ListNode removeDuplicateNodes(ListNode head) {
        if (head == null || head.next == null) return head;
        BitSet set = new BitSet();
        ListNode tail = head;
        set.set(head.val, true);
        while (tail.next != null) {
            if (!set.get(tail.next.val)) {
                set.set(tail.next.val, true);
                tail = tail.next;
            } else {
                tail.next = tail.next.next;
            }
        }
        return head;
    }
}