Q221 最大正方形
在一个由 0 和 1 组成的二维矩阵内,找到只包含 1 的最大正方形,并返回其面积。
示例:
输入:
1 0 1 0 0
1 0 1 1 1
1 1 1 1 1
1 0 0 1 0
输出: 4
class Solution {
public int maximalSquare(char[][] matrix) {
if (matrix == null || matrix.length == 0 || matrix[0].length == 0)
return 0;
int max = 0;
int[] heights = new int[matrix[0].length];
for (char[] line : matrix) {
for (int i = 0; i < line.length; i++)
heights[i] = line[i] == '0' ? 0 : heights[i] + 1;
int temp = findMaxSize(heights);
max = max > temp ? max : temp;
}
return max;
}
private int findMaxSize(int[] heights) {
Deque<Integer> stack = new LinkedList<>();
int maxSize = 0;
for (int i = 0; i < heights.length; i++) {
while (!stack.isEmpty() && heights[stack.peek()] > heights[i]) {
int t = stack.pop();
int left = stack.isEmpty() ? - 1 : stack.peek();
int right = i;
int minLength = heights[t] < right - left - 1 ? heights[t] : right - left - 1;
maxSize = maxSize > minLength * minLength ? maxSize : minLength * minLength;
}
stack.push(i);
}
while (!stack.isEmpty()) {
int t = stack.pop();
int left = stack.isEmpty() ? t - 1 : stack.peek();
int right = heights.length - 1;
int minLength = heights[t] < right - left ? heights[t] : right - left;
maxSize = maxSize > minLength * minLength ? maxSize : minLength * minLength;
}
return maxSize;
}
}