feat: add solutions to lc problem: No.2609

yanglbme · yanglbme · commit f31bc2af419c · 2023-04-02T19:58:48.000+08:00
No.2609.Find the Longest Balanced Substring of a Binary String
diff --git a/solution/2600-2699/2609.Find the Longest Balanced Substring of a Binary String/README.md b/solution/2600-2699/2609.Find the Longest Balanced Substring of a Binary String/README.md
@@ -53,6 +53,25 @@
 
 <!-- 这里可写通用的实现逻辑 -->
 
+**方法一：暴力枚举**
+
+注意到数据范围很小，因此，我们可以枚举所有的子串 $s[i..j]$，检查其是否为平衡子串，如果是，则更新答案。
+
+时间复杂度 $O(n^3)$，空间复杂度 $O(1)$。其中 $n$ 为字符串 $s$ 的长度。
+
+**方法二：枚举优化**
+
+我们用变量 $zero$ 和 $one$ 分别记录当前连续的 $0$ 和 $1$ 的个数。
+
+遍历字符串 $s$，对于当前字符 $c$：
+
+-   如果当前字符为 `'0'`，我们判断此时 $one$ 是否大于 $0$，是则将 $zero$ 和 $one$ 重置为 $0$，接下来将 $zero$ 加 $1$。
+-   如果当前字符为 `'1'`，则将 $one$ 加 $1$，并更新答案为 $2 \times min(one, zero)$。
+
+遍历结束后，即可得到最长的平衡子串的长度。
+
+时间复杂度 $O(n)$，空间复杂度 $O(1)$。其中 $n$ 为字符串 $s$ 的长度。
+
 <!-- tabs:start -->
 
 ### **Python3**
@@ -80,6 +99,21 @@ class Solution:
         return ans
 ```
 
+```python
+class Solution:
+    def findTheLongestBalancedSubstring(self, s: str) -> int:
+        ans = zero = one = 0
+        for c in s:
+            if c == '0':
+                if one:
+                    zero = one = 0
+                zero += 1
+            else:
+                one += 1
+                ans = max(ans, 2 * min(one, zero))
+        return ans
+```
+
 ### **Java**
 
 <!-- 这里可写当前语言的特殊实现逻辑 -->
@@ -113,6 +147,27 @@ class Solution {
 }
 ```
 
+```java
+class Solution {
+    public int findTheLongestBalancedSubstring(String s) {
+        int zero = 0, one = 0;
+        int ans = 0, n = s.length();
+        for (int i = 0; i < n; ++i) {
+            if (s.charAt(i) == '0') {
+                if (one > 0) {
+                    zero = 0;
+                    one = 0;
+                }
+                ++zero;
+            } else {
+                ans = Math.max(ans, 2 * Math.min(zero, ++one));
+            }
+        }
+        return ans;
+    }
+}
+```
+
 ### **C++**
 
 ```cpp
@@ -144,6 +199,28 @@ public:
 };
 ```
 
+```cpp
+class Solution {
+public:
+    int findTheLongestBalancedSubstring(string s) {
+        int zero = 0, one = 0;
+        int ans = 0, n = s.size();
+        for (char& c : s) {
+            if (c == '0') {
+                if (one > 0) {
+                    zero = 0;
+                    one = 0;
+                }
+                ++zero;
+            } else {
+                ans = max(ans, 2 * min(zero, ++one));
+            }
+        }
+        return ans;
+    }
+};
+```
+
 ### **Go**
 
 ```go
@@ -178,6 +255,38 @@ func max(a, b int) int {
 }
 ```
 
+```go
+func findTheLongestBalancedSubstring(s string) (ans int) {
+	zero, one := 0, 0
+	for _, c := range s {
+		if c == '0' {
+			if one > 0 {
+				zero, one = 0, 0
+			}
+			zero++
+		} else {
+			one++
+			ans = max(ans, 2*min(zero, one))
+		}
+	}
+	return
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}
+```
+
 ### **...**
 
 ```
diff --git a/solution/2600-2699/2609.Find the Longest Balanced Substring of a Binary String/README_EN.md b/solution/2600-2699/2609.Find the Longest Balanced Substring of a Binary String/README_EN.md
@@ -72,6 +72,21 @@ class Solution:
         return ans
 ```
 
+```python
+class Solution:
+    def findTheLongestBalancedSubstring(self, s: str) -> int:
+        ans = zero = one = 0
+        for c in s:
+            if c == '0':
+                if one:
+                    zero = one = 0
+                zero += 1
+            else:
+                one += 1
+                ans = max(ans, 2 * min(one, zero))
+        return ans
+```
+
 ### **Java**
 
 ```java
@@ -103,6 +118,27 @@ class Solution {
 }
 ```
 
+```java
+class Solution {
+    public int findTheLongestBalancedSubstring(String s) {
+        int zero = 0, one = 0;
+        int ans = 0, n = s.length();
+        for (int i = 0; i < n; ++i) {
+            if (s.charAt(i) == '0') {
+                if (one > 0) {
+                    zero = 0;
+                    one = 0;
+                }
+                ++zero;
+            } else {
+                ans = Math.max(ans, 2 * Math.min(zero, ++one));
+            }
+        }
+        return ans;
+    }
+}
+```
+
 ### **C++**
 
 ```cpp
@@ -134,6 +170,28 @@ public:
 };
 ```
 
+```cpp
+class Solution {
+public:
+    int findTheLongestBalancedSubstring(string s) {
+        int zero = 0, one = 0;
+        int ans = 0, n = s.size();
+        for (char& c : s) {
+            if (c == '0') {
+                if (one > 0) {
+                    zero = 0;
+                    one = 0;
+                }
+                ++zero;
+            } else {
+                ans = max(ans, 2 * min(zero, ++one));
+            }
+        }
+        return ans;
+    }
+};
+```
+
 ### **Go**
 
 ```go
@@ -168,6 +226,38 @@ func max(a, b int) int {
 }
 ```
 
+```go
+func findTheLongestBalancedSubstring(s string) (ans int) {
+	zero, one := 0, 0
+	for _, c := range s {
+		if c == '0' {
+			if one > 0 {
+				zero, one = 0, 0
+			}
+			zero++
+		} else {
+			one++
+			ans = max(ans, 2*min(zero, one))
+		}
+	}
+	return
+}
+
+func max(a, b int) int {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}
+```
+
 ### **...**
 
 ```
diff --git a/solution/2600-2699/2609.Find the Longest Balanced Substring of a Binary String/Solution.cpp b/solution/2600-2699/2609.Find the Longest Balanced Substring of a Binary String/Solution.cpp
@@ -1,24 +1,17 @@
 class Solution {
 public:
     int findTheLongestBalancedSubstring(string s) {
-        int n = s.size();
-        int ans = 0;
-        auto check = [&](int i, int j) -> bool {
-            int cnt = 0;
-            for (int k = i; k <= j; ++k) {
-                if (s[k] == '1') {
-                    ++cnt;
-                } else if (cnt) {
-                    return false;
-                }
-            }
-            return cnt * 2 == j - i + 1;
-        };
-        for (int i = 0; i < n; ++i) {
-            for (int j = i + 1; j < n; ++j) {
-                if (check(i, j)) {
-                    ans = max(ans, j - i + 1);
+        int zero = 0, one = 0;
+        int ans = 0, n = s.size();
+        for (char& c : s) {
+            if (c == '0') {
+                if (one > 0) {
+                    zero = 0;
+                    one = 0;
                 }
+                ++zero;
+            } else {
+                ans = max(ans, 2 * min(zero, ++one));
             }
         }
         return ans;
diff --git a/solution/2600-2699/2609.Find the Longest Balanced Substring of a Binary String/Solution.go b/solution/2600-2699/2609.Find the Longest Balanced Substring of a Binary String/Solution.go
@@ -1,21 +1,14 @@
 func findTheLongestBalancedSubstring(s string) (ans int) {
-	n := len(s)
-	check := func(i, j int) bool {
-		cnt := 0
-		for k := i; k <= j; k++ {
-			if s[k] == '1' {
-				cnt++
-			} else if cnt > 0 {
-				return false
-			}
-		}
-		return cnt*2 == j-i+1
-	}
-	for i := 0; i < n; i++ {
-		for j := i + 1; j < n; j++ {
-			if check(i, j) {
-				ans = max(ans, j-i+1)
+	zero, one := 0, 0
+	for _, c := range s {
+		if c == '0' {
+			if one > 0 {
+				zero, one = 0, 0
 			}
+			zero++
+		} else {
+			one++
+			ans = max(ans, 2*min(zero, one))
 		}
 	}
 	return
@@ -26,4 +19,11 @@ func max(a, b int) int {
 		return a
 	}
 	return b
+}
+
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
 }
diff --git a/solution/2600-2699/2609.Find the Longest Balanced Substring of a Binary String/Solution.java b/solution/2600-2699/2609.Find the Longest Balanced Substring of a Binary String/Solution.java
@@ -1,26 +1,18 @@
 class Solution {
     public int findTheLongestBalancedSubstring(String s) {
-        int n = s.length();
-        int ans = 0;
+        int zero = 0, one = 0;
+        int ans = 0, n = s.length();
         for (int i = 0; i < n; ++i) {
-            for (int j = i + 1; j < n; ++j) {
-                if (check(s, i, j)) {
-                    ans = Math.max(ans, j - i + 1);
+            if (s.charAt(i) == '0') {
+                if (one > 0) {
+                    zero = 0;
+                    one = 0;
                 }
+                ++zero;
+            } else {
+                ans = Math.max(ans, 2 * Math.min(zero, ++one));
             }
         }
         return ans;
     }
-    
-    private boolean check(String s, int i, int j) {
-        int cnt = 0;
-        for (int k = i; k <= j; ++k) {
-            if (s.charAt(k) == '1') {
-                ++cnt;
-            } else if (cnt > 0) {
-                return false;
-            }
-        }
-        return cnt * 2 == j - i + 1;
-    }
 }
diff --git a/solution/2600-2699/2609.Find the Longest Balanced Substring of a Binary String/Solution.py b/solution/2600-2699/2609.Find the Longest Balanced Substring of a Binary String/Solution.py

-Original file line number
+Diff line change
 class Solution:
     def findTheLongestBalancedSubstring(self, s: str) -> int:
 -        def check(i, j):
 -            cnt = 0
 -            for k in range(i, j + 1):
 -                if s[k] == '1':
 -                    cnt += 1
 -                elif cnt:
 -                    return False
 -            return cnt * 2 == (j - i + 1)
+-
 -        n = len(s)
 -        ans = 0
 -        for i in range(n):
 -            for j in range(i + 1, n):
 -                if check(i, j):
 -                    ans = max(ans, j - i + 1)
 +        ans = zero = one = 0
 +        for c in s:
 +            if c == '0':
 +                if one:
 +                    zero = one = 0
 +                zero += 1
 +            else:
 +                one += 1
 +                ans = max(ans, 2 * min(one, zero))
         return ans