solution.java

public class Solution {
    public int solution(int[] radiuses) {
        int length = radiuses.length;
        int[] startCounts = new int[length];
        int[] endCounts = new int[length];

        // make sure there's no overflows
        for (int i = 0; i < length; i++) {
            radiuses[i] = Math.min(length, radiuses[i]);
        }

        int lastPos = length - 1;
        for (int i = 0; i < length; i++) {
            int radius = radiuses[i];
            int startPos = Math.max(i - radius, 0);
            int endPos = Math.min(i + radius, lastPos);

            startCounts[startPos]++;
            endCounts[endPos]++;
        }

        // printAll(startCounts);
        // printAll(endCounts);

        int intersectCount = 0;
        int currentLayerCount = 0;

        for (int i = 0; i < length; i++) {
            int newStarts = startCounts[i];
            int newEnds = endCounts[i];

            intersectCount += newStarts * currentLayerCount + (newStarts * (newStarts - 1)) / 2;
            currentLayerCount = currentLayerCount + newStarts - newEnds;

            // short circuit return
            if(intersectCount > 10000000) {
                return -1;
            }
        }

        return intersectCount;
    }

    public void printAll(int[] numbers) {
        int length = numbers.length;
        for (int i = 0; i < length; i++) {
            System.out.println(numbers[i]);
        }

        System.out.println("");
    }
}