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g2001_2100.s2055_plates_between_candles.Solution Maven / Gradle / Ivy

package g2001_2100.s2055_plates_between_candles;

// #Medium #Array #String #Binary_Search #Prefix_Sum
// #2022_05_26_Time_10_ms_(92.49%)_Space_164.8_MB_(5.53%)

public class Solution {
    public int[] platesBetweenCandles(String s, int[][] queries) {
        char[] sa = s.toCharArray();
        int n = sa.length;
        int[] nextCandle = new int[n + 1];
        nextCandle[n] = -1;
        for (int i = n - 1; i >= 0; i--) {
            nextCandle[i] = sa[i] == '|' ? i : nextCandle[i + 1];
        }
        int[] prevCandle = new int[n];
        int[] prevPlates = new int[n];
        int countPlate = 0;
        if (sa[0] == '*') {
            countPlate = 1;
            prevCandle[0] = -1;
        }
        for (int i = 1; i < n; i++) {
            if (sa[i] == '|') {
                prevCandle[i] = i;
                prevPlates[i] = countPlate;
            } else {
                prevCandle[i] = prevCandle[i - 1];
                countPlate++;
            }
        }
        int len = queries.length;
        int[] res = new int[len];
        for (int i = 0; i < len; i++) {
            int[] query = queries[i];
            int start = query[0];
            int end = query[1];
            int curPlates = 0;
            int endCandle = prevCandle[end];
            if (endCandle >= start) {
                int startCandle = nextCandle[start];

                curPlates = prevPlates[endCandle] - prevPlates[startCandle];
            }
            res[i] = curPlates;
        }
        return res;
    }
}