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January 20, 2019 07:42
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Максимальная площадь прямоугольника в квадратной матрице за O(N^3)
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package ru.drone.ya; | |
public class MaxRectangleN3 { | |
/** | |
* Максимальная площадь прямоугольника в квадратной матрице | |
*/ | |
public long getMaxRectangleSquare(int[][] m) { | |
int[] cursor = new int[m.length]; | |
long max = 0; | |
for (int row = 0; row < m.length; row++) { | |
for (int i = 0; i < cursor.length; i++) | |
cursor[i] = m[row][i] == 0 ? 0 : cursor[i] + 1; | |
max = Long.max(max, getMaxRectangleSquare(cursor)); | |
} | |
return max; | |
} | |
/** a - строка с высотами*/ | |
private long getMaxRectangleSquare(int[] a) { | |
long maxSq = a[0]; | |
for (int left = 0; left < a.length; left++) { | |
long minH = a[left];//минимальная высота на отрезке от left до right | |
for (int right = left; right < a.length; right++) { | |
minH = Long.min(minH, a[right]); | |
maxSq = Long.max(maxSq, minH * (1 + right - left)); | |
} | |
} | |
return maxSq; | |
} | |
public static void main(String[] args) { | |
int[][] m = new int[][]{ | |
{1, 1, 1, 1, 1}, | |
{1, 1, 1, 1, 1}, | |
{1, 1, 1, 1, 1}, | |
{1, 1, 1, 1, 1}, | |
{1, 1, 1, 1, 1} | |
}; | |
System.out.println("TEST 1 expected: 25, actual: " + new MaxRectangleN3().getMaxRectangleSquare(m)); | |
m = new int[][]{ | |
{0, 0, 1, 1, 1}, | |
{0, 0, 1, 0, 1}, | |
{1, 1, 1, 1, 0}, | |
{1, 0, 1, 1, 1}, | |
{1, 1, 1, 1, 0} | |
}; | |
System.out.println("TEST 2 expected: 6, actual: " + new MaxRectangleN3().getMaxRectangleSquare(m)); | |
m = new int[][]{ | |
{0, 1, 1, 1, 1}, | |
{1, 1, 1, 1, 1}, | |
{1, 1, 1, 1, 1}, | |
{1, 1, 1, 1, 1}, | |
{1, 1, 1, 0, 1} | |
}; | |
System.out.println("TEST 3 expected: 16, actual: " + new MaxRectangleN3().getMaxRectangleSquare(m)); | |
} | |
} |
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