|
| 1 | +--- |
| 2 | +comments: true |
| 3 | +difficulty: Medium |
| 4 | +edit_url: https://github.com/doocs/leetcode/edit/main/solution/1100-1199/1143.Longest%20Common%20Subsequence/README_EN.md |
| 5 | +tags: |
| 6 | + - String |
| 7 | + - Dynamic Programming |
| 8 | +--- |
| 9 | + |
| 10 | +<!-- problem:start --> |
| 11 | + |
| 12 | +# [1143. Longest Common Subsequence](https://leetcode.com/problems/longest-common-subsequence) |
| 13 | + |
| 14 | +[中文文档](/solution/1100-1199/1143.Longest%20Common%20Subsequence/README.md) |
| 15 | + |
| 16 | +## Description |
| 17 | + |
| 18 | +<!-- description:start --> |
| 19 | + |
| 20 | +<p>Given two strings <code>text1</code> and <code>text2</code>, return <em>the length of their longest <strong>common subsequence</strong>. </em>If there is no <strong>common subsequence</strong>, return <code>0</code>.</p> |
| 21 | + |
| 22 | +<p>A <strong>subsequence</strong> of a string is a new string generated from the original string with some characters (can be none) deleted without changing the relative order of the remaining characters.</p> |
| 23 | + |
| 24 | +<ul> |
| 25 | + <li>For example, <code>"ace"</code> is a subsequence of <code>"abcde"</code>.</li> |
| 26 | +</ul> |
| 27 | + |
| 28 | +<p>A <strong>common subsequence</strong> of two strings is a subsequence that is common to both strings.</p> |
| 29 | + |
| 30 | +<p> </p> |
| 31 | +<p><strong class="example">Example 1:</strong></p> |
| 32 | + |
| 33 | +<pre> |
| 34 | +<strong>Input:</strong> text1 = "abcde", text2 = "ace" |
| 35 | +<strong>Output:</strong> 3 |
| 36 | +<strong>Explanation:</strong> The longest common subsequence is "ace" and its length is 3. |
| 37 | +</pre> |
| 38 | + |
| 39 | +<p><strong class="example">Example 2:</strong></p> |
| 40 | + |
| 41 | +<pre> |
| 42 | +<strong>Input:</strong> text1 = "abc", text2 = "abc" |
| 43 | +<strong>Output:</strong> 3 |
| 44 | +<strong>Explanation:</strong> The longest common subsequence is "abc" and its length is 3. |
| 45 | +</pre> |
| 46 | + |
| 47 | +<p><strong class="example">Example 3:</strong></p> |
| 48 | + |
| 49 | +<pre> |
| 50 | +<strong>Input:</strong> text1 = "abc", text2 = "def" |
| 51 | +<strong>Output:</strong> 0 |
| 52 | +<strong>Explanation:</strong> There is no such common subsequence, so the result is 0. |
| 53 | +</pre> |
| 54 | + |
| 55 | +<p> </p> |
| 56 | +<p><strong>Constraints:</strong></p> |
| 57 | + |
| 58 | +<ul> |
| 59 | + <li><code>1 <= text1.length, text2.length <= 1000</code></li> |
| 60 | + <li><code>text1</code> and <code>text2</code> consist of only lowercase English characters.</li> |
| 61 | +</ul> |
| 62 | + |
| 63 | +<!-- description:end --> |
| 64 | + |
| 65 | +## Solutions |
| 66 | + |
| 67 | +<!-- solution:start --> |
| 68 | + |
| 69 | +### Solution 1: Dynamic Programming |
| 70 | + |
| 71 | +We define $f[i][j]$ as the length of the longest common subsequence of the first $i$ characters of $text1$ and the first $j$ characters of $text2$. Therefore, the answer is $f[m][n]$, where $m$ and $n$ are the lengths of $text1$ and $text2$, respectively. |
| 72 | + |
| 73 | +If the $i$th character of $text1$ and the $j$th character of $text2$ are the same, then $f[i][j] = f[i - 1][j - 1] + 1$; if the $i$th character of $text1$ and the $j$th character of $text2$ are different, then $f[i][j] = max(f[i - 1][j], f[i][j - 1])$. The state transition equation is: |
| 74 | + |
| 75 | +$$ |
| 76 | +f[i][j] = |
| 77 | +\begin{cases} |
| 78 | +f[i - 1][j - 1] + 1, & \textit{if } text1[i - 1] = text2[j - 1] \\ |
| 79 | +\max(f[i - 1][j], f[i][j - 1]), & \textit{if } text1[i - 1] \neq text2[j - 1] |
| 80 | +\end{cases} |
| 81 | +$$ |
| 82 | + |
| 83 | +The time complexity is $O(m \times n)$, and the space complexity is $O(m \times n)$. Here, $m$ and $n$ are the lengths of $text1$ and $text2$, respectively. |
| 84 | + |
| 85 | +<!-- tabs:start --> |
| 86 | + |
| 87 | +#### Python3 |
| 88 | + |
| 89 | +```python |
| 90 | +class Solution: |
| 91 | + def longestCommonSubsequence(self, text1: str, text2: str) -> int: |
| 92 | + m, n = len(text1), len(text2) |
| 93 | + f = [[0] * (n + 1) for _ in range(m + 1)] |
| 94 | + for i in range(1, m + 1): |
| 95 | + for j in range(1, n + 1): |
| 96 | + if text1[i - 1] == text2[j - 1]: |
| 97 | + f[i][j] = f[i - 1][j - 1] + 1 |
| 98 | + else: |
| 99 | + f[i][j] = max(f[i - 1][j], f[i][j - 1]) |
| 100 | + return f[m][n] |
| 101 | +``` |
| 102 | + |
| 103 | +#### Java |
| 104 | + |
| 105 | +```java |
| 106 | +class Solution { |
| 107 | + public int longestCommonSubsequence(String text1, String text2) { |
| 108 | + int m = text1.length(), n = text2.length(); |
| 109 | + int[][] f = new int[m + 1][n + 1]; |
| 110 | + for (int i = 1; i <= m; ++i) { |
| 111 | + for (int j = 1; j <= n; ++j) { |
| 112 | + if (text1.charAt(i - 1) == text2.charAt(j - 1)) { |
| 113 | + f[i][j] = f[i - 1][j - 1] + 1; |
| 114 | + } else { |
| 115 | + f[i][j] = Math.max(f[i - 1][j], f[i][j - 1]); |
| 116 | + } |
| 117 | + } |
| 118 | + } |
| 119 | + return f[m][n]; |
| 120 | + } |
| 121 | +} |
| 122 | +``` |
| 123 | + |
| 124 | +#### C++ |
| 125 | + |
| 126 | +```cpp |
| 127 | +class Solution { |
| 128 | +public: |
| 129 | + int longestCommonSubsequence(string text1, string text2) { |
| 130 | + int m = text1.size(), n = text2.size(); |
| 131 | + int f[m + 1][n + 1]; |
| 132 | + memset(f, 0, sizeof f); |
| 133 | + for (int i = 1; i <= m; ++i) { |
| 134 | + for (int j = 1; j <= n; ++j) { |
| 135 | + if (text1[i - 1] == text2[j - 1]) { |
| 136 | + f[i][j] = f[i - 1][j - 1] + 1; |
| 137 | + } else { |
| 138 | + f[i][j] = max(f[i - 1][j], f[i][j - 1]); |
| 139 | + } |
| 140 | + } |
| 141 | + } |
| 142 | + return f[m][n]; |
| 143 | + } |
| 144 | +}; |
| 145 | +``` |
| 146 | +
|
| 147 | +#### Go |
| 148 | +
|
| 149 | +```go |
| 150 | +func longestCommonSubsequence(text1 string, text2 string) int { |
| 151 | + m, n := len(text1), len(text2) |
| 152 | + f := make([][]int, m+1) |
| 153 | + for i := range f { |
| 154 | + f[i] = make([]int, n+1) |
| 155 | + } |
| 156 | + for i := 1; i <= m; i++ { |
| 157 | + for j := 1; j <= n; j++ { |
| 158 | + if text1[i-1] == text2[j-1] { |
| 159 | + f[i][j] = f[i-1][j-1] + 1 |
| 160 | + } else { |
| 161 | + f[i][j] = max(f[i-1][j], f[i][j-1]) |
| 162 | + } |
| 163 | + } |
| 164 | + } |
| 165 | + return f[m][n] |
| 166 | +} |
| 167 | +``` |
| 168 | + |
| 169 | +#### TypeScript |
| 170 | + |
| 171 | +```ts |
| 172 | +function longestCommonSubsequence(text1: string, text2: string): number { |
| 173 | + const m = text1.length; |
| 174 | + const n = text2.length; |
| 175 | + const f = Array.from({ length: m + 1 }, () => Array(n + 1).fill(0)); |
| 176 | + for (let i = 1; i <= m; i++) { |
| 177 | + for (let j = 1; j <= n; j++) { |
| 178 | + if (text1[i - 1] === text2[j - 1]) { |
| 179 | + f[i][j] = f[i - 1][j - 1] + 1; |
| 180 | + } else { |
| 181 | + f[i][j] = Math.max(f[i - 1][j], f[i][j - 1]); |
| 182 | + } |
| 183 | + } |
| 184 | + } |
| 185 | + return f[m][n]; |
| 186 | +} |
| 187 | +``` |
| 188 | + |
| 189 | +#### Rust |
| 190 | + |
| 191 | +```rust |
| 192 | +impl Solution { |
| 193 | + pub fn longest_common_subsequence(text1: String, text2: String) -> i32 { |
| 194 | + let (m, n) = (text1.len(), text2.len()); |
| 195 | + let (text1, text2) = (text1.as_bytes(), text2.as_bytes()); |
| 196 | + let mut f = vec![vec![0; n + 1]; m + 1]; |
| 197 | + for i in 1..=m { |
| 198 | + for j in 1..=n { |
| 199 | + f[i][j] = if text1[i - 1] == text2[j - 1] { |
| 200 | + f[i - 1][j - 1] + 1 |
| 201 | + } else { |
| 202 | + f[i - 1][j].max(f[i][j - 1]) |
| 203 | + }; |
| 204 | + } |
| 205 | + } |
| 206 | + f[m][n] |
| 207 | + } |
| 208 | +} |
| 209 | +``` |
| 210 | + |
| 211 | +#### JavaScript |
| 212 | + |
| 213 | +```js |
| 214 | +/** |
| 215 | + * @param {string} text1 |
| 216 | + * @param {string} text2 |
| 217 | + * @return {number} |
| 218 | + */ |
| 219 | +var longestCommonSubsequence = function (text1, text2) { |
| 220 | + const m = text1.length; |
| 221 | + const n = text2.length; |
| 222 | + const f = Array.from({ length: m + 1 }, () => Array(n + 1).fill(0)); |
| 223 | + for (let i = 1; i <= m; ++i) { |
| 224 | + for (let j = 1; j <= n; ++j) { |
| 225 | + if (text1[i - 1] == text2[j - 1]) { |
| 226 | + f[i][j] = f[i - 1][j - 1] + 1; |
| 227 | + } else { |
| 228 | + f[i][j] = Math.max(f[i - 1][j], f[i][j - 1]); |
| 229 | + } |
| 230 | + } |
| 231 | + } |
| 232 | + return f[m][n]; |
| 233 | +}; |
| 234 | +``` |
| 235 | + |
| 236 | +#### C# |
| 237 | + |
| 238 | +```cs |
| 239 | +public class Solution { |
| 240 | + public int LongestCommonSubsequence(string text1, string text2) { |
| 241 | + int m = text1.Length, n = text2.Length; |
| 242 | + int[,] f = new int[m + 1, n + 1]; |
| 243 | + for (int i = 1; i <= m; ++i) { |
| 244 | + for (int j = 1; j <= n; ++j) { |
| 245 | + if (text1[i - 1] == text2[j - 1]) { |
| 246 | + f[i, j] = f[i - 1, j - 1] + 1; |
| 247 | + } else { |
| 248 | + f[i, j] = Math.Max(f[i - 1, j], f[i, j - 1]); |
| 249 | + } |
| 250 | + } |
| 251 | + } |
| 252 | + return f[m, n]; |
| 253 | + } |
| 254 | +} |
| 255 | +``` |
| 256 | + |
| 257 | +#### Kotlin |
| 258 | + |
| 259 | +```kotlin |
| 260 | +class Solution { |
| 261 | + fun longestCommonSubsequence(text1: String, text2: String): Int { |
| 262 | + val m = text1.length |
| 263 | + val n = text2.length |
| 264 | + val f = Array(m + 1) { IntArray(n + 1) } |
| 265 | + for (i in 1..m) { |
| 266 | + for (j in 1..n) { |
| 267 | + if (text1[i - 1] == text2[j - 1]) { |
| 268 | + f[i][j] = f[i - 1][j - 1] + 1 |
| 269 | + } else { |
| 270 | + f[i][j] = Math.max(f[i - 1][j], f[i][j - 1]) |
| 271 | + } |
| 272 | + } |
| 273 | + } |
| 274 | + return f[m][n] |
| 275 | + } |
| 276 | +} |
| 277 | +``` |
| 278 | + |
| 279 | +<!-- tabs:end --> |
| 280 | + |
| 281 | +<!-- solution:end --> |
| 282 | + |
| 283 | +<!-- problem:end --> |
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