Session 43: DP 5

Original Session

Date: 16 Feb 2025

Topic: DP

Concept:

Programs

1526. Minimum Number of Increments on Subarrays to Form a Target Array.

leetcode here

    public int minNumberOperations(int[] target) {
        
        int ans = target[0];

        for (int i=1; i<target.length; i++) {

            if (target[i] > target[i-1]) {
                ans += target[i] - target[i-1];
            }
        }
        return ans;
    }

1653. Minimum Deletions to Make String Balanced.

leetcode here

public int minimumDeletions(String s) {
    
    int n = s.length();
    int aCount = 0;
    for (int i=0; i<n; i++) {

        if (s.charAt(i) == 'a') {
            aCount ++;
        }
    }

    int bCount = 0, ans = aCount;
    for (int i=0; i<n; i++) {

        if (s.charAt(i) == 'a') {
            aCount --;
        }

        ans = Math.min(ans, aCount + bCount);
        if (s.charAt(i) == 'b') {
            bCount ++;
        }
    }
    return ans;
}

1987. Number of Unique Good Subsequences

leetcode here

public int numberOfUniqueGoodSubsequences(String binary) {
    
    int mod = 1000000007;
    int endWithOne = 0;
    int endWithZero = 0;
    int hasZero = 0;

    for (int i=0; i<binary.length(); i++) {

        if (binary.charAt(i) == '1') {

            endWithOne = (endWithOne + endWithZero + 1) % mod;
        } else {

            hasZero = 1;
            endWithZero = (endWithOne + endWithZero) % mod;
        }
    }

    return (endWithOne + endWithZero + hasZero) % mod;
}

87. Scramble String

leetcode here

public boolean isScramble(String s1, String s2) {
    if (s1.equals(s2)) return true;
    if (s1.length() != s2.length()) return false;

    String key = s1 + "#" + s2;
    if (dp.containsKey(key)) return dp.get(key);

    int n = s1.length();

    // Check if both strings have the same character counts (anagram check)
    int[] freq = new int[26];
    for (int i = 0; i < n; i++) {
        freq[s1.charAt(i) - 'a']++;
        freq[s2.charAt(i) - 'a']--;
    }
    for (int count : freq) {
        if (count != 0) {
            dp.put(key, false);
            return false;
        }
    }

    for (int i = 1; i < n; i++) {
        // Case 1: No Swap
        if (isScramble(s1.substring(0, i), s2.substring(0, i)) &&
            isScramble(s1.substring(i), s2.substring(i))) {
            dp.put(key, true);
            return true;
        }

        // Case 2: Swap
        if (isScramble(s1.substring(0, i), s2.substring(n - i)) &&
            isScramble(s1.substring(i), s2.substring(0, n - i))) {
            dp.put(key, true);
            return true;
        }
    }

    dp.put(key, false);
    return false;
}
}

Programs

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