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Java Solution for LeetCode algorithm problems, continually updating
package g0401_0500.s0427_construct_quad_tree;
// #Medium #Array #Tree #Matrix #Divide_and_Conquer
public class Solution {
public Node construct(int[][] grid) {
return optimizedDfs(grid, 0, 0, grid.length);
}
private Node optimizedDfs(int[][] grid, int rowStart, int colStart, int len) {
int zeroCount = 0;
int oneCount = 0;
for (int row = rowStart; row < rowStart + len; row++) {
boolean isBreak = false;
for (int col = colStart; col < colStart + len; col++) {
if (grid[row][col] == 0) {
zeroCount++;
} else {
oneCount++;
}
if (oneCount > 0 && zeroCount > 0) {
// We really no need to scan all.
// Once we know there are both 0 and 1 then we can break.
isBreak = true;
break;
}
}
if (isBreak) {
break;
}
}
if (oneCount > 0 && zeroCount > 0) {
int midLen = len / 2;
Node topLeft = optimizedDfs(grid, rowStart, colStart, midLen);
Node topRight = optimizedDfs(grid, rowStart, colStart + midLen, midLen);
Node bottomLeft = optimizedDfs(grid, rowStart + midLen, colStart, midLen);
Node bottomRight = optimizedDfs(grid, rowStart + midLen, colStart + midLen, midLen);
boolean isLeaf = false;
return new Node(true, isLeaf, topLeft, topRight, bottomLeft, bottomRight);
} else {
boolean resultVal = oneCount > 0;
boolean isLeaf = true;
return new Node(resultVal, isLeaf);
}
}
}