41 lines
1.0 KiB
Java
41 lines
1.0 KiB
Java
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public class ConvexHullOptimization {
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long[] A = new long[1000000];
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long[] B = new long[1000000];
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int len;
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int ptr;
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// a descends
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public void addLine(long a, long b) {
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// intersection of (A[len-2],B[len-2]) with (A[len-1],B[len-1]) must lie to the left of intersection of (A[len-1],B[len-1]) with (a,b)
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while (len >= 2 && (B[len - 2] - B[len - 1]) * (a - A[len - 1]) >= (B[len - 1] - b) * (A[len - 1] - A[len - 2])) {
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--len;
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}
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A[len] = a;
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B[len] = b;
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++len;
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}
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// x ascends
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public long minValue(long x) {
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ptr = Math.min(ptr, len - 1);
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while (ptr + 1 < len && A[ptr + 1] * x + B[ptr + 1] <= A[ptr] * x + B[ptr]) {
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++ptr;
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}
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return A[ptr] * x + B[ptr];
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}
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// Usage example
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public static void main(String[] args) {
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ConvexHullOptimization h = new ConvexHullOptimization();
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h.addLine(3, 0);
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h.addLine(2, 1);
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h.addLine(3, 2);
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h.addLine(0, 6);
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System.out.println(h.minValue(0));
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System.out.println(h.minValue(1));
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System.out.println(h.minValue(2));
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System.out.println(h.minValue(3));
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}
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}
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