leetcode 497, 528. Random Point in Non-overlapping Rectangles | 497. 非重叠矩形中的随机点（Java）

497. Random Point in Non-overlapping Rectangles

https://leetcode.com/problems/random-point-in-non-overlapping-rectangles/

题解

大坑：面积包含边界，计算要注意+1，这种随机数的问题，没有固定的输出，调bug不好调啊…目前的方法是，手动指定random的值，遍历所有可能的random，看是否符合预期。

思路：
1、先按照面积计算每个rectangle的权重
2、根据权重选择rectangle的下标（参考 528. Random Pick with Weight）
3、选好rectangle后，根据范围随机生成横坐标x、纵坐标y

class Solution {Random r;int N;int[][] rects;long[] weight; // 权重long[] weightSum; // 权重前缀和public Solution(int[][] rects) {this.rects = rects;r = new Random();N = rects.length;weight = new long[N];weightSum = new long[N];for (int i = 0; i < N; i++) {weight[i] = ((long) rects[i][2] + 1 - rects[i][0]) * ((long) rects[i][3] + 1 - rects[i][1]); // +1 因为包含边界！坑！！}weightSum[0] = 0;if (N > 1) weightSum[1] = weight[0];for (int i = 2; i < N; i++) {weightSum[i] = weightSum[i - 1] + weight[i - 1];}}public int[] pick() {// 根据权重选择一个rectanglelong sum = weight[N - 1] + weightSum[N - 1];long rand = randLong(0, sum);// 反向查找randLong属于的indexint L = 0;int R = N - 1;int index = -1;if (weightSum[N - 1] <= rand) {index = N - 1;} else {while (L < R) {int M = L + (R - L) / 2;if (weightSum[M] == rand) {index = M;break;} else if (weightSum[M] < rand) {if (L == M) {index = M;break;}L = M;} else {R = M - 1;if (weightSum[R] <= rand) {index = R;break;}}}if (index == -1) index = L;}int[] rec = rects[index];long x = randLong(rec[0], rec[2] + 1);long y = randLong(rec[1], rec[3] + 1);return new int[]{(int) x, (int) y};}public long randLong(long a, long b) { // 左闭右开return a + (long) (Math.random() * (b - a));}}/*** Your Solution object will be instantiated and called as such:* Solution obj = new Solution(rects);* int[] param_1 = obj.pick();*/

528. Random Pick with Weight

https://leetcode.com/problems/random-pick-with-weight/

本题是上一题的一个子问题，直接复制粘贴了。

class Solution {int N;int[] w; // 权重int[] wSum; // 权重前缀和public Solution(int[] w) {N = w.length;this.w = w;wSum = new int[N];wSum[0] = 0;if (N > 1) wSum[1] = this.w[0];for (int i = 2; i < N; i++) {wSum[i] = wSum[i - 1] + this.w[i - 1];}}public int pickIndex() {// 根据权重选择一个rectangleint sum = w[N - 1] + wSum[N - 1];int rand = rand(0, sum);// 反向查找randLong属于的indexint L = 0;int R = N - 1;int index = -1;if (wSum[N - 1] <= rand) {index = N - 1;} else {while (L < R) {int M = L + (R - L) / 2;if (wSum[M] == rand) {index = M;break;} else if (wSum[M] < rand) {if (L == M) {index = M;break;}L = M;} else {R = M - 1;if (wSum[R] <= rand) {index = R;break;}}}if (index == -1) index = L;}return index;}public int rand(int a, int b) { // 左闭右开return (int) (a + (Math.random() * (b - a)));}
}/*** Your Solution object will be instantiated and called as such:* Solution obj = new Solution(w);* int param_1 = obj.pickIndex();*/

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leetcode 497, 528. Random Point in Non-overlapping Rectangles | 497. 非重叠矩形中的随机点（Java）

497. Random Point in Non-overlapping Rectangles

题解

528. Random Pick with Weight

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