算法奇妙屋(2)-模拟

一. 力扣6. Z 字形变换

1. 题目

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2. 算法原理

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3. 代码

    public String convert(String s, int numRows) {if (numRows == 1) {return s;}int len = s.length();int d = 2 * numRows - 2;StringBuffer ret = new StringBuffer();for (int i = 0; i < len; i += d) {ret.append(s.charAt(i));}for (int k = 1; k < numRows - 1; k++) {for (int i = k, j = d - i; i < len || j < len; i += d, j += d) {if (i < len) {ret.append(s.charAt(i));}if (j < len) {ret.append(s.charAt(j));}}}for (int i = numRows - 1; i < len; i += d) {ret.append(s.charAt(i));}return ret.toString();}

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二. 力扣38. 外观数列

1. 题目

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2. 算法原理

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3. 代码

    public String countAndSay(int n) {String ret = "1";for (int i = 1; i < n; i++) {StringBuilder ss = new StringBuilder();int left = 0;int right = 0;int len = ret.length();while(left < len && right < len) {while(left < len && right < len && ret.charAt(right) == ret.charAt(left)) {right++;}ss.append(Integer.toString(right - left));ss.append(ret.charAt(left));left = right;}ret = ss.toString();}return ret;}

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三. 力扣495. 提莫攻击

1. 题目

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2. 算法原理

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3. 代码

    public int findPoisonedDuration(int[] timeSeries, int duration) {int ret = 0;for (int i = 1; i < timeSeries.length; i++) {int tmp = timeSeries[i] - timeSeries[i - 1];if (tmp >= duration) {ret += duration;}else {ret += tmp;}}ret += duration;return ret;}

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四. 力扣1419. 数青蛙

1. 题目

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2. 算法原理

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3. 代码1(暴力通俗易懂)

    public int minNumberOfFrogs(String croakOfFrogs) {int[] arr = new int[128];for (int i = 0; i < croakOfFrogs.length(); i++) {char ch = croakOfFrogs.charAt(i);if (ch == 'c') {if (arr['k'] == 0) {arr['c']++;}else {arr['k']--;arr['c']++;}}else if (ch == 'r') {if (arr['c'] != 0) {arr['c']--;arr['r']++;}else {return -1;}}else if (ch == 'o') {if (arr['r'] != 0) {arr['r']--;arr['o']++;}else {return -1;}}else if (ch == 'a') {if (arr['o'] != 0) {arr['o']--;arr['a']++;}else {return -1;}}else if (ch == 'k') {if (arr['a'] != 0) {arr['a']--;arr['k']++;}else {return -1;}}}if (arr['c'] != 0 || arr['r'] != 0 || arr['o'] != 0 || arr['a'] != 0) {return -1;}return arr['k'];}

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4. 代码2(哈希映射)

    public int minNumberOfFrogs(String croakOfFrogs) {char[] c = croakOfFrogs.toCharArray();String s = "croak";int n = s.length();int[] hash = new int[n];HashMap<Character,Integer> map = new HashMap<>();for (int i = 0; i < n; i++) {map.put(s.charAt(i),i); // 哈希表中让哈希值key与下标value对应}for (char ch : c) {int index = map.get(ch);if (index == 0) {if (hash[n - 1] != 0) {hash[n - 1]--;}hash[index]++;}else {if (hash[index - 1] != 0) {hash[index - 1]--;hash[index]++;}else {return -1;}}}for (int i = 0; i < n - 1; i++) {if (hash[i] != 0) {return -1;}}return hash[n - 1];}