From f06c2431f69ad2cc8f596d9e5cab79d05d3008ae Mon Sep 17 00:00:00 2001
From: YDZ <ydz627@gmail.com>
Date: Sat, 8 Jun 2019 14:24:59 +0800
Subject: [PATCH] =?UTF-8?q?=E6=B7=BB=E5=8A=A0=20problem=20424?=
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---
 ...Longest Repeating Character Replacement.go | 15 +++++
 ...st Repeating Character Replacement_test.go | 63 +++++++++++++++++++
 .../README.md                                 | 49 +++++++++++++++
 3 files changed, 127 insertions(+)
 create mode 100644 Algorithms/424. Longest Repeating Character Replacement/424. Longest Repeating Character Replacement.go
 create mode 100644 Algorithms/424. Longest Repeating Character Replacement/424. Longest Repeating Character Replacement_test.go
 create mode 100644 Algorithms/424. Longest Repeating Character Replacement/README.md

diff --git a/Algorithms/424. Longest Repeating Character Replacement/424. Longest Repeating Character Replacement.go b/Algorithms/424. Longest Repeating Character Replacement/424. Longest Repeating Character Replacement.go
new file mode 100644
index 00000000..874b0028
--- /dev/null
+++ b/Algorithms/424. Longest Repeating Character Replacement/424. Longest Repeating Character Replacement.go	
@@ -0,0 +1,15 @@
+package leetcode
+
+func characterReplacement(s string, k int) int {
+	res, left, right, counter, freq := 0, 0, 1, 0, make([]int, 26)
+	for right = 0; right < len(s); right++ {
+		freq[s[right]-'A']++
+		counter = max(counter, freq[s[right]-'A'])
+		for right-left+1-counter > k {
+			freq[s[left]-'A']--
+			left++
+		}
+		res = max(res, right-left+1)
+	}
+	return res
+}
diff --git a/Algorithms/424. Longest Repeating Character Replacement/424. Longest Repeating Character Replacement_test.go b/Algorithms/424. Longest Repeating Character Replacement/424. Longest Repeating Character Replacement_test.go
new file mode 100644
index 00000000..2c3d5bd3
--- /dev/null
+++ b/Algorithms/424. Longest Repeating Character Replacement/424. Longest Repeating Character Replacement_test.go	
@@ -0,0 +1,63 @@
+package leetcode
+
+import (
+	"fmt"
+	"testing"
+)
+
+type question424 struct {
+	para424
+	ans424
+}
+
+// para 是参数
+// one 代表第一个参数
+type para424 struct {
+	s string
+	k int
+}
+
+// ans 是答案
+// one 代表第一个答案
+type ans424 struct {
+	one int
+}
+
+func Test_Problem424(t *testing.T) {
+
+	qs := []question424{
+
+		question424{
+			para424{"AABABBA", 1},
+			ans424{4},
+		},
+
+		question424{
+			para424{"ABBB", 2},
+			ans424{4},
+		},
+
+		question424{
+			para424{"BAAA", 0},
+			ans424{3},
+		},
+
+		question424{
+			para424{"ABCDE", 1},
+			ans424{2},
+		},
+
+		question424{
+			para424{"BAAAB", 2},
+			ans424{5},
+		},
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 424------------------------\n")
+
+	for _, q := range qs {
+		_, p := q.ans424, q.para424
+		fmt.Printf("【input】:%v       【output】:%v\n", p, characterReplacement(p.s, p.k))
+	}
+	fmt.Printf("\n\n\n")
+}
diff --git a/Algorithms/424. Longest Repeating Character Replacement/README.md b/Algorithms/424. Longest Repeating Character Replacement/README.md
new file mode 100644
index 00000000..8b962472
--- /dev/null
+++ b/Algorithms/424. Longest Repeating Character Replacement/README.md	
@@ -0,0 +1,49 @@
+# [424. Longest Repeating Character Replacement](https://leetcode.com/problems/longest-repeating-character-replacement/)
+
+## 题目
+
+
+Given a string that consists of only uppercase English letters, you can replace any letter in the string with another letter at most k times. Find the length of a longest substring containing all repeating letters you can get after performing the above operations.
+
+Note:  
+
+Both the string's length and k will not exceed 10^4.
+
+Example 1:
+
+```c
+Input:
+s = "ABAB", k = 2
+
+Output:
+4
+
+Explanation:
+Replace the two 'A's with two 'B's or vice versa.
+```
+
+Example 2:
+
+```c
+Input:
+s = "AABABBA", k = 1
+
+Output:
+4
+
+Explanation:
+Replace the one 'A' in the middle with 'B' and form "AABBBBA".
+The substring "BBBB" has the longest repeating letters, which is 4.
+```
+
+
+
+## 题目大意
+
+
+给一个字符串和变换次数 K，要求经过 K 次字符转换以后，输出相同字母能出现连续最长的长度。
+
+
+这道题笔者也提交了好几遍才通过。这一题是考察滑动窗口的题目，但是不能单纯的把左右窗口往右移动。因为有可能存在 ABBBBBA 的情况，这种情况需要从两边方向同时判断。正确的滑动窗口的做法应该是，边滑动的过程中边统计出现频次最多的字母，因为最后求得的最长长度的解，一定是在出现频次最多的字母上，再改变其他字母得到的最长连续长度。窗口滑动的过程中，用窗口的长度减去窗口中出现频次最大的长度，如果差值比 K 大，就代表需要缩小左窗口了直到差值等于 K。res 不断的取出窗口的长度的最大值就可以了。
+
+