528. Random Pick with Weight
Explanation
To solve this problem, we need to generate a random index based on the weights provided in the input array. We can achieve this by creating a prefix sum array to store the cumulative sum of weights. We then generate a random number between 1 and the total sum of weights, and find the index where this random number falls in the prefix sum array.
import java.util.Random;
class Solution {
int[] prefixSum;
Random rand;
public Solution(int[] w) {
prefixSum = new int[w.length];
rand = new Random();
prefixSum[0] = w[0];
for (int i = 1; i < w.length; i++) {
prefixSum[i] = prefixSum[i - 1] + w[i];
}
}
public int pickIndex() {
int totalSum = prefixSum[prefixSum.length - 1];
int randNum = rand.nextInt(totalSum) + 1;
int left = 0, right = prefixSum.length - 1;
while (left < right) {
int mid = left + (right - left) / 2;
if (prefixSum[mid] < randNum) {
left = mid + 1;
} else {
right = mid;
}
}
return left;
}
}Code Editor (Testing phase)
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