LeetCode 956: Tallest Billboard Solution

Master LeetCode problem 956 (Tallest Billboard), a hard challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

956. Tallest Billboard

Hard

Array Dynamic Programming

Problem Explanation

Explanation:

To solve this problem, we can use dynamic programming. We need to keep track of the possible heights achievable using the rods given. We can represent this using a map where the key is the difference in heights between the two supports and the value is the maximum achievable height. By iterating through each rod and updating the map, we can determine the maximum height of the billboard installation.

Create a map to store the possible heights achievable.
Iterate through each rod and update the map with the current rod's height.
For each existing height h in the map, update the map with the current rod's height added to h (representing the same height on both supports) and the absolute difference between the current rod's height and h (representing different heights on both supports).
The final result would be the maximum achievable height stored in the map.

Time complexity: O(n * sum), where n is the number of rods and sum is the sum of all rod lengths. Space complexity: O(sum), where sum is the sum of all rod lengths.

Solution Code

class Solution {
    public int tallestBillboard(int[] rods) {
        Map<Integer, Integer> dp = new HashMap<>();
        dp.put(0, 0);
        
        for (int rod : rods) {
            Map<Integer, Integer> cur = new HashMap<>(dp);
            for (Map.Entry<Integer, Integer> entry : cur.entrySet()) {
                int h = entry.getKey();
                dp.put(h + rod, Math.max(dp.getOrDefault(h + rod, 0), entry.getValue()));
                dp.put(Math.abs(h - rod), Math.max(dp.getOrDefault(Math.abs(h - rod), 0), Math.min(h, entry.getValue() + rod)));
            }
        }
        
        return dp.get(0);
    }
}

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