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_554.java
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_554.java
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package com.fishercoder.solutions;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class _554 {
public static class Solution1 {
/**
* credit: https://leetcode.com/articles/brick-wall/
* <p>
* we make use of a HashMap
* map which is used to store entries in the form:
* (sum,count). Here,
* sum refers to the cumulative sum of the bricks' widths encountered in the current row, and
* count refers to the number of times the corresponding sum is obtained. Thus,
* sum in a way, represents the positions of the bricks's boundaries relative to the leftmost boundary.
* <p>
* This is done based on the following observation:
* We will never obtain the same value of sum twice while traversing over a particular row.
* Thus, if the sum value is repeated while traversing over the rows, it means some row's brick boundary coincides with some previous row's brick boundary.
* This fact is accounted for by incrementing the corresponding count value.
* But, for every row, we consider the sum only upto the second last brick, since the last boundary isn't a valid boundary for the solution.
*/
public int leastBricks(List<List<Integer>> wall) {
Map<Integer, Integer> map = new HashMap();
for (List<Integer> row : wall) {
int sum = 0;
for (int i = 0; i < row.size() - 1; i++) {
//NOTE: i < row.size()-1
sum += row.get(i);
if (map.containsKey(sum)) {
map.put(sum, map.get(sum) + 1);
} else {
map.put(sum, 1);
}
}
}
int result = wall.size();
for (int key : map.keySet()) {
result = Math.min(result, wall.size() - map.get(key));
}
return result;
}
}
}