c++版 nms

 定义的box是左上角的x、y以及宽度w、高度h

 iou计算出来的交集的w、h必须判断是否大于0，这避免了两个框没有交集的情况。如果不判断，可能存在w、h都为负生成iou>0的情况进而影响结果。

 +1操作是计算像素点个数，这个地方其实有点没太理解到，但开源的代码都是这么写的。

#include<iostream>
#include<vector>
#include<algorithm>
#include <stdio.h>
#include <stdlib.h>
using namespace std;


typedef struct Bbox{
    int x;
    int y;
    int w;
    int h;
    float score;
}Bbox;

class Solution {
public:

    static bool sort_score(Bbox box1,Bbox box2){
        return box1.score > box2.score ? true : false;
    }


    float iou(Bbox box1,Bbox box2){
        int x1 = max(box1.x,box2.x);
        int y1 = max(box1.y,box2.y);
        int x2 = min(box1.x+box1.w,box2.x+box2.w);
        int y2 = min(box1.y+box1.h,box2.y+box2.h);
        int w = max(0,x2 - x1 + 1);
        int h = max(0,y2 - y1 + 1);
        float over_area = w*h;
        return over_area/(box1.w * box1.h + box2.w * box2.h - over_area);
    }

    vector<Bbox> nms(std::vector<Bbox>&vec_boxs,float threshold){
        vector<Bbox>results;
        std::sort(vec_boxs.begin(),vec_boxs.end(),sort_score);
        while(vec_boxs.size() > 0)
        {
            results.push_back(vec_boxs[0]);
            int index = 1;
            while(index < vec_boxs.size()){
                float iou_value = iou(vec_boxs[0],vec_boxs[index]);
                cout << "iou:" << iou_value << endl;
                if(iou_value > threshold)
                    vec_boxs.erase(vec_boxs.begin() + index);
                else
                    index++;
            }
            vec_boxs.erase(vec_boxs.begin());
        }
        return results;
    }
};

int main(){
    Solution a;
    vector<Bbox> input;

    // Bbox box1 = {1,1,1,1,0.3};
    // Bbox box2 = {0,0,2,2,0.4};
    //Bbox box1 = {1,3,2,2,0.3};        //iou为负
    //Bbox box2 = {0,0,2,2,0.4};
    //Bbox box1 = {4,4,2,2,0.3};
    //Bbox box2 = {0,0,2,2,0.4};
    // Bbox box1 = {4,4,1,1,0.3};
    // Bbox box2 = {0,0,2,2,0.4};
    // Bbox box1 = {3,3,1,1,0.3};
    // Bbox box2 = {0,0,2,2,0.4};
    input.push_back(box1);
    input.push_back(box2);
    vector<Bbox> res;
    res = a.nms(input,0.3);
    // for(int i = 0;i < res.size();i++){
    //     printf("%d %d %d %d %f",res[i].x,res[i].y,res[i].w,res[i].h,res[i].score);
    //     cout << endl;
    // }
    return 0;
}