Merge branch 'DaleStudy:main' into main

Author: std-freejia

best-time-to-buy-and-sell-stock/delight010.swift

@@ -0,0 +1,12 @@
+class Solution {
+    func maxProfit(_ prices: [Int]) -> Int {
+        var lowPrice: Int = prices[0]
+        var maxProfit: Int = 0
+        for i in 0..<prices.endIndex {
+            lowPrice = min(lowPrice, prices[i])
+            maxProfit = max(maxProfit, prices[i] - lowPrice)
+        }
+        return maxProfit
+    }
+}
+ 

best-time-to-buy-and-sell-stock/hoyeongkwak.py

@@ -0,0 +1,29 @@
+'''
+time complexity : O(n)
+space complexity : O(2n)
+
+Algorithm : dp
+주식 보유하는 경우:
+- 이전에 이미 보유 : hold[i - 1]
+- i번째 날 새로 사는 경우 : -prices[i]
+
+주식을 팔았을 떄:
+- 이전에 이미 팜 : sold[i - 1]
+- i번째 날 파는 경우 : hold[i-1] + prices[i]
+'''
+
+class Solution:
+    def maxProfit(self, prices: List[int]) -> int:
+        if not prices or len(prices) < 2:
+            return 0
+        n = len(prices)
+        hold = [0] * n
+        sold = [0] * n
+
+        hold[0] = -prices[0]
+        sold[0] = 0
+
+        for i in range(1, n):
+            hold[i] = max(hold[i - 1], -prices[i])
+            sold[i] = max(sold[i - 1], hold[i - 1] + prices[i])
+        return sold[n - 1]

best-time-to-buy-and-sell-stock/hu6r1s.py

@@ -0,0 +1,25 @@
+class Solution:
+    """
+    1. 브루트포스
+    2중 for문이라서 O(n^2)임.
+    prices의 길이가 10^5이므로 10^10이 되면서 시간초과가 발생
+
+    2. 이분탐색으로 가능할까 했지만 DP를 사용해야 하는 문제 같음
+    시간복잡도는 O(n)이 나옴
+    """
+    """
+    def maxProfit(self, prices: List[int]) -> int:
+        max_profit = 0
+        for i in range(len(prices)-1):
+            for j in range(i, len(prices)):
+                profit = prices[j] - prices[i]
+                max_profit = max(max_profit, profit)
+        return max_profit
+    """
+    def maxProfit(self, prices: List[int]) -> int:
+        max_profit = 0
+        min_price = prices[0]
+        for price in prices:
+            max_profit = max(max_profit, price - min_price)
+            min_price = min(price, min_price)
+        return max_profit

best-time-to-buy-and-sell-stock/hyer0705.ts

@@ -0,0 +1,14 @@
+function maxProfit(prices: number[]): number {
+  let minPrice = Infinity;
+  let maxProfit = 0;
+
+  for (const price of prices) {
+    if (price < minPrice) {
+      minPrice = price;
+    } else {
+      maxProfit = Math.max(maxProfit, price - minPrice);
+    }
+  }
+
+  return maxProfit;
+}

best-time-to-buy-and-sell-stock/njngwn.java

@@ -0,0 +1,16 @@
+// Time Complexity: O(n), n: prices.length
+// Space Complexity: O(1), because 3 int-variables are declared -> O(1)+O(1)+O(1)
+class Solution {
+    public int maxProfit(int[] prices) {
+        int buyPrice = prices[0];
+        int sellPrice = 0;
+        int profit = 0;  // store maxProfit
+
+        for (int i = 1; i < prices.length; ++i) {
+            buyPrice = Math.min(buyPrice, prices[i]);
+            profit = Math.max(profit, prices[i] - buyPrice);
+        }
+
+        return profit;
+    }
+}

best-time-to-buy-and-sell-stock/s0ooo0k.java

@@ -0,0 +1,14 @@
+class Solution {
+    public int maxProfit(int[] prices) {
+        int price = prices[0];
+        int maxProfit = 0;
+
+        for(int i=1; i<prices.length; i++){
+            int profit = prices[i]-price;
+            maxProfit = Math.max(maxProfit, profit);
+            price = Math.min(price, prices[i]);
+        }
+        return maxProfit;
+    }
+}
+

best-time-to-buy-and-sell-stock/yhkee0404.go

@@ -0,0 +1,9 @@
+func maxProfit(prices []int) int {
+    ans := 0
+    bought := prices[0]
+    for i := 1; i != len(prices); i++ {
+        ans = max(ans, prices[i] - bought)
+        bought = min(bought, prices[i])
+    }
+    return ans
+}

encode-and-decode-strings/hu6r1s.py

@@ -0,0 +1,14 @@
+class Solution:
+    """
+    @param: strs: a list of strings
+    @return: encodes a list of strings to a single string.
+    """
+    def encode(self, strs):
+        return "secretKey!@#".join(strs)
+
+    """
+    @param: str: A string
+    @return: decodes a single string to a list of strings
+    """
+    def decode(self, str):
+        return str.split("secretKey!@#")

encode-and-decode-strings/hyer0705.ts

@@ -0,0 +1,47 @@
+class Solution {
+  private DELIMITER = "*";
+
+  /**
+   * @param strs: a list of strings
+   * @returns: encodes a list of strings to a single string.
+   */
+  public encode(strs: string[]): string {
+    let encoded = "";
+
+    for (const str of strs) {
+      encoded += `${str.length}${this.DELIMITER}${str}`;
+    }
+
+    return encoded;
+  }
+
+  /**
+   * @param str: A string
+   * @returns: decodes a single string to a list of strings
+   */
+  public decode(str: string): string[] {
+    const decoded: string[] = [];
+
+    let stack: string[] = [];
+    let pointer = 0;
+
+    while (pointer < str.length) {
+      const char = str[pointer];
+
+      if (char === this.DELIMITER) {
+        let strLength: number = Number(stack.join(""));
+        stack = [];
+
+        const word = str.substring(pointer + 1, pointer + 1 + strLength);
+        pointer = pointer + 1 + strLength;
+
+        decoded.push(word);
+      } else {
+        stack.push(char);
+        pointer++;
+      }
+    }
+
+    return decoded;
+  }
+}

encode-and-decode-strings/yhkee0404.java

@@ -0,0 +1,44 @@
+public class Solution {
+    /*
+     * @param strs: a list of strings
+     * @return: encodes a list of strings to a single string.
+     */
+    public String encode(List<String> strs) {
+        // write your code here
+        return strs.parallelStream()
+                .map(s ->
+                    s.chars()
+                            .parallel()
+                            .mapToObj(c -> new StringBuilder(String.format("%02x", c)))
+                            .collect(
+                                StringBuilder::new,
+                                StringBuilder::append,
+                                (a, b) -> a.append(b)
+                            )
+                ).collect(
+                    StringBuilder::new,
+                    (a, b) -> a.append(b)
+                            .append(' '),
+                    (a, b) -> a.append(b)
+                ).toString();
+    }
+
+    /*
+     * @param str: A string
+     * @return: decodes a single string to a list of strings
+     */
+    public List<String> decode(String str) {
+        // write your code here
+        final List<String> ans = new ArrayList<>();
+        final StringTokenizer st = new StringTokenizer(str);
+        while (st.hasMoreTokens()) {
+            final String s = st.nextToken();
+            final StringBuilder sb = new StringBuilder();
+            for (int i = 0; i < s.length(); i += 2) {
+                sb.append((char) Integer.parseInt(s.substring(i, i + 2), 16));
+            }
+            ans.add(sb.toString());
+        }
+        return ans;
+    }
+}