题目:
题解:
java
class Solution {
Random rand;
List<Integer> arr;
int[][] rects;
public Solution(int[][] rects) {
rand = new Random();
arr = new ArrayList<Integer>();
arr.add(0);
this.rects = rects;
for (int[] rect : rects) {
int a = rect[0], b = rect[1], x = rect[2], y = rect[3];
arr.add(arr.get(arr.size() - 1) + (x - a + 1) * (y - b + 1));
}
}
public int[] pick() {
int k = rand.nextInt(arr.get(arr.size() - 1));
int rectIndex = binarySearch(arr, k + 1) - 1;
k -= arr.get(rectIndex);
int[] rect = rects[rectIndex];
int a = rect[0], b = rect[1], y = rect[3];
int col = y - b + 1;
int da = k / col;
int db = k - col * da;
return new int[]{a + da, b + db};
}
private int binarySearch(List<Integer> arr, int target) {
int low = 0, high = arr.size() - 1;
while (low <= high) {
int mid = (high - low) / 2 + low;
int num = arr.get(mid);
if (num == target) {
return mid;
} else if (num > target) {
high = mid - 1;
} else {
low = mid + 1;
}
}
return low;
}
}