108 lines
2.9 KiB
Java
108 lines
2.9 KiB
Java
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//给定一个正整数数组 w ，其中 w[i] 代表下标 i 的权重（下标从 0 开始），请写一个函数 pickIndex ，它可以随机地获取下标 i，选取下标
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//i 的概率与 w[i] 成正比。
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//
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//
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// 例如，对于 w = [1, 3]，挑选下标 0 的概率为 1 / (1 + 3) = 0.25 （即，25%），而选取下标 1 的概率为 3 / (1 +
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// 3) = 0.75（即，75%）。
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//
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// 也就是说，选取下标 i 的概率为 w[i] / sum(w) 。
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//
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//
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//
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// 示例 1：
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//
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// 输入：
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//["Solution","pickIndex"]
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//[[[1]],[]]
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//输出：
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//[null,0]
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//解释：
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//Solution solution = new Solution([1]);
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//solution.pickIndex(); // 返回 0，因为数组中只有一个元素，所以唯一的选择是返回下标 0。
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//
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// 示例 2：
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//
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// 输入：
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//["Solution","pickIndex","pickIndex","pickIndex","pickIndex","pickIndex"]
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//[[[1,3]],[],[],[],[],[]]
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//输出：
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//[null,1,1,1,1,0]
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//解释：
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//Solution solution = new Solution([1, 3]);
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//solution.pickIndex(); // 返回 1，返回下标 1，返回该下标概率为 3/4 。
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//solution.pickIndex(); // 返回 1
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//solution.pickIndex(); // 返回 1
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//solution.pickIndex(); // 返回 1
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//solution.pickIndex(); // 返回 0，返回下标 0，返回该下标概率为 1/4 。
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//
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//由于这是一个随机问题，允许多个答案，因此下列输出都可以被认为是正确的:
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//[null,1,1,1,1,0]
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//[null,1,1,1,1,1]
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//[null,1,1,1,0,0]
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//[null,1,1,1,0,1]
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//[null,1,0,1,0,0]
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//......
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//诸若此类。
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//
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//
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//
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//
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// 提示：
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//
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//
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// 1 <= w.length <= 10000
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// 1 <= w[i] <= 10^5
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// pickIndex 将被调用不超过 10000 次
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//
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// Related Topics 数学 二分查找 前缀和 随机化 👍 143 👎 0
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package leetcode.editor.cn;
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//528:按权重随机选择
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class RandomPickWithWeight {
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public static void main(String[] args) {
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//测试代码
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// Solution solution = new RandomPickWithWeight().new Solution();
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}
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//力扣代码
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//leetcode submit region begin(Prohibit modification and deletion)
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class Solution {
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private int[] arr;
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private int[] weight;
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public Solution(int[] w) {
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arr = w;
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weight = new int[w.length];
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weight[0] = arr[0];
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for (int i = 1; i < arr.length; i++) {
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weight[i] = weight[i - 1] + arr[i];
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}
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}
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public int pickIndex() {
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int start = 0;
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int end = weight.length - 1;
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int max = (int) (Math.random() * weight[end]) + 1;
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while (start < end) {
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int mid = (end - start) / 2 + start;
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if (weight[mid] < max) {
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start = mid + 1;
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} else {
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end = mid;
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}
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}
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return start;
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}
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}
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/**
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* Your Solution object will be instantiated and called as such:
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* Solution obj = new Solution(w);
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* int param_1 = obj.pickIndex();
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*/
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//leetcode submit region end(Prohibit modification and deletion)
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}
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