g0001_0100.s0042_trapping_rain_water.Solution.c Maven / Gradle / Ivy

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104 LeetCode algorithm problem solutions

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// #Hard #Top_100_Liked_Questions #Top_Interview_Questions #Array #Dynamic_Programming #Two_Pointers
// #Stack #Monotonic_Stack #Dynamic_Programming_I_Day_9 #Udemy_Two_Pointers
// #Big_O_Time_O(n)_Space_O(1) #2024_10_30_Time_0_ms_(100.00%)_Space_9.6_MB_(64.92%)

#include 

int trap(int* height, int heightSize) {
    int l = 0;
    int r = heightSize - 1;
    int res = 0;
    int lowerWall = 0;

    while (l < r) {
        int lVal = height[l];
        int rVal = height[r];

        // Determine which side has the lower wall and add water accordingly
        if (lVal < rVal) {
            // Update lower wall height if lVal has increased
            lowerWall = lVal > lowerWall ? lVal : lowerWall;
            // Add the trapped water at this position
            res += lowerWall - lVal;
            // Move left pointer
            l++;
        } else {
            // Update lower wall height if rVal has increased
            lowerWall = rVal > lowerWall ? rVal : lowerWall;
            // Add the trapped water at this position
            res += lowerWall - rVal;
            // Move right pointer
            r--;
        }
    }

    return res;
}