Merge branch 'youngyangyang04:master' into master

Author: zrzhit

problems/0053.最大子序和.md

@@ -240,6 +240,42 @@ class Solution:
             res = max(res, dp[i])
         return res
 ```
+
+动态规划
+
+```python
+class Solution:
+    def maxSubArray(self, nums):
+        if not nums:
+            return 0
+        dp = [0] * len(nums)    # dp[i]表示包括i之前的最大连续子序列和
+        dp[0] = nums[0]
+        result = dp[0]
+        for i in range(1, len(nums)):
+            dp[i] = max(dp[i-1]+nums[i], nums[i])   # 状态转移公式
+            if dp[i] > result:
+                result = dp[i]                      # result 保存dp[i]的最大值
+        return result
+```
+
+动态规划优化
+
+```python
+class Solution:
+    def maxSubArray(self, nums: List[int]) -> int:
+        max_sum = float("-inf") # 初始化结果为负无穷大，方便比较取最大值
+        current_sum = 0         # 初始化当前连续和
+
+        for num in nums:
+
+            # 更新当前连续和
+            # 如果原本的连续和加上当前数字之后没有当前数字大，说明原本的连续和是负数，那么就直接从当前数字开始重新计算连续和
+            current_sum = max(current_sum+num, num) 
+            max_sum = max(max_sum, current_sum) # 更新结果
+
+        return max_sum
+```
+
 ### Go
 贪心法
 ```go

problems/0055.跳跃游戏.md

@@ -143,6 +143,23 @@ class Solution:
         return False
 ```
 
+```python
+## 基于当前最远可到达位置判断
+class Solution:
+    def canJump(self, nums: List[int]) -> bool:
+        far = nums[0]
+        for i in range(len(nums)):
+            # 要考虑两个情况
+            # 1. i <= far - 表示 当前位置i 可以到达
+            # 2. i > far - 表示 当前位置i 无法到达
+            if i > far:
+                return False
+            far = max(far, nums[i]+i)
+        # 如果循环正常结束，表示最后一个位置也可以到达，否则会在中途直接退出
+        # 关键点在于，要想明白其实列表中的每个位置都是需要验证能否到达的
+        return True
+```
+
 ### Go
 
 ```go

problems/0135.分发糖果.md

@@ -177,21 +177,20 @@ class Solution {
 ```python
 class Solution:
     def candy(self, ratings: List[int]) -> int:
-        candyVec = [1] * len(ratings)
+        n = len(ratings)
+        candies = [1] * n
 
-        # 从前向后遍历，处理右侧比左侧评分高的情况
-        for i in range(1, len(ratings)):
+        # Forward pass: handle cases where right rating is higher than left
+        for i in range(1, n):
             if ratings[i] > ratings[i - 1]:
-                candyVec[i] = candyVec[i - 1] + 1
+                candies[i] = candies[i - 1] + 1
 
-        # 从后向前遍历，处理左侧比右侧评分高的情况
-        for i in range(len(ratings) - 2, -1, -1):
+        # Backward pass: handle cases where left rating is higher than right
+        for i in range(n - 2, -1, -1):
             if ratings[i] > ratings[i + 1]:
-                candyVec[i] = max(candyVec[i], candyVec[i + 1] + 1)
+                candies[i] = max(candies[i], candies[i + 1] + 1)
 
-        # 统计结果
-        result = sum(candyVec)
-        return result
+        return sum(candies)
 
 ```
 

problems/0150.逆波兰表达式求值.md

@@ -108,7 +108,7 @@ public:
             }
         }
 
-        int result = st.top();
+        long long result = st.top();
         st.pop(); // 把栈里最后一个元素弹出（其实不弹出也没事）
         return result;
     }

problems/1047.删除字符串中的所有相邻重复项.md

@@ -164,7 +164,7 @@ class Solution {
         int top = -1;
         for (int i = 0; i < s.length(); i++) {
             char c = s.charAt(i);
-            // 当 top > 0,即栈中有字符时，当前字符如果和栈中字符相等，弹出栈顶字符，同时 top--
+            // 当 top >= 0,即栈中有字符时，当前字符如果和栈中字符相等，弹出栈顶字符，同时 top--
             if (top >= 0 && res.charAt(top) == c) {
                 res.deleteCharAt(top);
                 top--;

problems/kamacoder/0099.岛屿的数量深搜.md

@@ -412,6 +412,46 @@ const dfs = (graph, visited, x, y) => {
 ### Swift
 
 ### Scala
+```scala
+import util.control.Breaks._
+
+object Solution {
+    val dir = List((-1,0), (0,-1), (1,0), (0,1)) // 四个方向
+
+    def dfs(grid: Array[Array[Char]], visited: Array[Array[Boolean]], row: Int, col: Int): Unit = {
+        (0 until 4).map { x =>
+            val nextR = row + dir(x)(0)
+            val nextC = col + dir(x)(1)
+            breakable {
+                if(nextR < 0 || nextR >= grid.length || nextC < 0 || nextC >= grid(0).length) break
+                if (!visited(nextR)(nextC) && grid(nextR)(nextC) == '1') {
+                    visited(nextR)(nextC) = true // 经过就记录
+                    dfs(grid, visited, nextR, nextC)
+                }
+            }
+        }
+    }
+
+    def numIslands(grid: Array[Array[Char]]): Int = {
+        val row = grid.length
+        val col = grid(0).length
+        var visited = Array.fill(row)(Array.fill(col)(false))
+        var counter = 0
+
+        (0 until row).map{ r =>
+            (0 until col).map{ c =>
+                if (!visited(r)(c) && grid(r)(c) == '1') {
+                    visited(r)(c) = true // 经过就记录
+                    dfs(grid, visited, r, c)
+                    counter += 1
+                }
+            }
+        }
+        
+        counter
+    }
+}
+```
 
 ### C#