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102 lines
3.8 KiB
C++
102 lines
3.8 KiB
C++
/**********************************************************************
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* File: dppoint.h
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* Description: Simple generic dynamic programming class.
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* Author: Ray Smith
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* Created: Wed Mar 25 18:57:01 PDT 2009
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*
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* (C) Copyright 2009, Google Inc.
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** Licensed under the Apache License, Version 2.0 (the "License");
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** you may not use this file except in compliance with the License.
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** You may obtain a copy of the License at
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** http://www.apache.org/licenses/LICENSE-2.0
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** Unless required by applicable law or agreed to in writing, software
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** distributed under the License is distributed on an "AS IS" BASIS,
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** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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** See the License for the specific language governing permissions and
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** limitations under the License.
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*
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**********************************************************************/
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#ifndef TESSERACT_CCSTRUCT_DPPOINT_H_
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#define TESSERACT_CCSTRUCT_DPPOINT_H_
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#include "host.h"
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namespace tesseract {
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// A simple class to provide a dynamic programming solution to a class of
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// 1st-order problems in which the cost is dependent only on the current
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// step and the best cost to that step, with a possible special case
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// of using the variance of the steps, and only the top choice is required.
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// Useful for problems such as finding the optimal cut points in a fixed-pitch
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// (vertical or horizontal) situation.
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// Skeletal Example:
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// DPPoint* array = new DPPoint[width];
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// for (int i = 0; i < width; i++) {
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// array[i].AddLocalCost(cost_at_i)
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// }
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// DPPoint* best_end = DPPoint::Solve(..., array);
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// while (best_end != NULL) {
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// int cut_index = best_end - array;
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// best_end = best_end->best_prev();
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// }
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// delete [] array;
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class DPPoint {
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public:
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// The cost function evaluates the total cost at this (excluding this's
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// local_cost) and if it beats this's total_cost, then
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// replace the appropriate values in this.
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typedef inT64 (DPPoint::*CostFunc)(const DPPoint* prev);
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DPPoint()
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: local_cost_(0), total_cost_(MAX_INT32), total_steps_(1), best_prev_(NULL),
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n_(0), sig_x_(0), sig_xsq_(0) {
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}
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// Solve the dynamic programming problem for the given array of points, with
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// the given size and cost function.
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// Steps backwards are limited to being between min_step and max_step
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// inclusive.
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// The return value is the tail of the best path.
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static DPPoint* Solve(int min_step, int max_step, bool debug,
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CostFunc cost_func, int size, DPPoint* points);
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// A CostFunc that takes the variance of step into account in the cost.
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inT64 CostWithVariance(const DPPoint* prev);
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// Accessors.
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int total_cost() const {
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return total_cost_;
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}
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int Pathlength() const {
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return total_steps_;
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}
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const DPPoint* best_prev() const {
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return best_prev_;
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}
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void AddLocalCost(int new_cost) {
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local_cost_ += new_cost;
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}
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private:
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// Code common to different cost functions.
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// Update the other members if the cost is lower.
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void UpdateIfBetter(inT64 cost, inT32 steps, const DPPoint* prev,
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inT32 n, inT32 sig_x, inT64 sig_xsq);
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inT32 local_cost_; // Cost of this point on its own.
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inT32 total_cost_; // Sum of all costs in best path to here.
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// During cost calculations local_cost is excluded.
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inT32 total_steps_; // Number of steps in best path to here.
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const DPPoint* best_prev_; // Pointer to prev point in best path from here.
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// Information for computing the variance part of the cost.
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inT32 n_; // Number of steps in best path to here for variance.
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inT32 sig_x_; // Sum of step sizes for computing variance.
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inT64 sig_xsq_; // Sum of squares of steps for computing variance.
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};
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} // namespace tesseract.
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#endif // TESSERACT_CCSTRUCT_DPPOINT_H_
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