2022-06-13

1143. Longest Common Subsequence

Description

Given two strings text1 and text2, return the length of their longest common subsequence. If there is no common subsequence, return 0.

A subsequence 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.

• For example, "ace" is a subsequence of "abcde".

A common subsequence of two strings is a subsequence that is common to both strings.

Example 1:

Input: text1 = "abcde", text2 = "ace" 
Output: 3  
Explanation: The longest common subsequence is "ace" and its length is 3.

Example 2:

Input: text1 = "abc", text2 = "abc"
Output: 3
Explanation: The longest common subsequence is "abc" and its length is 3.

Example 3:

Input: text1 = "abc", text2 = "def"
Output: 0
Explanation: There is no such common subsequence, so the result is 0. 

Constraints:

• 1 <= text1.length, text2.length <= 1000

• text1 and text2 consist of only lowercase English characters.

Solution

Approach #0

func longestCommonSubsequence(text1 string, text2 string) int {
    m, n := len(text1), len(text2)
    dp := make([][]int, m+1)
    for i := 0; i < m+1; i++ {
        dp[i] = make([]int, n+1)
    }
    for i, c1 := range text1 {
        for j, c2 := range text2 {
            if c1 == c2 {
                dp[i+1][j+1] = dp[i][j] + 1
            } else {
                dp[i+1][j+1] = max(dp[i][j+1], dp[i+1][j])
            }
        }
    }
    return dp[m][n]
}

func max(a, b int) int {
    if a > b {
        return a
    }
    return b
}

583. Delete Operation for Two Strings

Description

Given two strings word1 and word2, return the minimum number of steps required to make word1 and word2 the same.

In one step, you can delete exactly one character in either string.

Example 1:

Input: word1 = "sea", word2 = "eat"
Output: 2
Explanation: You need one step to make "sea" to "ea" and another step to make "eat" to "ea".

Example 2:

Input: word1 = "leetcode", word2 = "etco"
Output: 4

Constraints:

• 1 <= word1.length, word2.length <= 500

• word1 and word2 consist of only lowercase English letters.

Solution

Approach #0: Just find the longest common subsequence

func minDistance(word1 string, word2 string) int {
    m, n := len(word1), len(word2)
    dp := make([][]int, m+1)
    for i := 0; i < m+1; i++ {
        dp[i] = make([]int, n+1)
    }
    for i, c1 := range word1 {
        for j, c2 := range word2 {
            if c1 == c2 {
                dp[i+1][j+1] = dp[i][j] + 1
            } else {
                dp[i+1][j+1] = max(dp[i][j+1], dp[i+1][j])
            }
        }
    }
    return m + n - 2*dp[m][n]
}

func max(a, b int) int {
    if a > b {
        return a
    }
    return b
}

Approach #1

func minDistance(word1 string, word2 string) int {
    m, n := len(word1), len(word2)
    dp := make([][]int, m+1)
    for i := 0; i < m+1; i++ {
        dp[i] = make([]int, n+1)
        dp[i][0]=i
    }
    for j:=0;j<n+1;j++ {
        dp[0][j]=j
    }
    for i, c1 := range word1 {
        for j, c2 := range word2 {
            if c1 == c2 {
                dp[i+1][j+1] = dp[i][j]
            } else {
                dp[i+1][j+1] = min(dp[i][j+1], dp[i+1][j])+1
            }
        }
    }
    return dp[m][n]
}

func min(a, b int) int {
    if a < b {
        return a
    }
    return b
}

1051. Height Checker

Description

A school is trying to take an annual photo of all the students. The students are asked to stand in a single file line in non-decreasing order by height. Let this ordering be represented by the integer array expected where expected[i] is the expected height of the ith student in line.

You are given an integer array heights representing the current order that the students are standing in. Each heights[i] is the height of the ith student in line (0-indexed).

Return the number of indices where heights[i] != expected[i].

Example 1:

Input: heights = [1,1,4,2,1,3]
Output: 3
Explanation: 
heights:  [1,1,4,2,1,3]
expected: [1,1,1,2,3,4]
Indices 2, 4, and 5 do not match.

Example 2:

Input: heights = [5,1,2,3,4]
Output: 5
Explanation:
heights:  [5,1,2,3,4]
expected: [1,2,3,4,5]
All indices do not match.

Example 3:

Input: heights = [1,2,3,4,5]
Output: 0
Explanation:
heights:  [1,2,3,4,5]
expected: [1,2,3,4,5]
All indices match.

Constraints:

• 1 <= heights.length <= 100

• 1 <= heights[i] <= 100

Solution

Approach #0

func heightChecker(heights []int) (ans int) {
    expected := append([]int(nil), heights...)
    sort.Ints(expected)
    for i, h := range heights {
        if h != expected[i] {
            ans++
        }
    }
    return
}

Approach #1

func heightChecker(heights []int) (ans int) {
    cnt := make([]int, 101)
    for _, h := range heights {
        cnt[h]++
    }
    index := 0
    for i, c := range cnt {
        for ; c > 0; c-- {
            if heights[index] != i {
                ans++
            }
            index++
        }
    }
    return
}