Can someone tell me what this program is doing line by line? [closed]

This program is trying to determine the fitness of a puzzle by determining the number of conflicts in a puzzle (how many duplicate entries there are in each row, column, and 3- by-3 block). A solved Sudoku should have a "howFit" value of zero.

#include "Sudoku.h"
#include "SudokuFitness.h"
int howFit(shared_ptr<Puzzle> &_p) {
// cast to Sudoku Puzzle
shared_ptr<Sudoku> p = dynamic_pointer_cast<Sudoku>(_p);
int tot = 0;

// update tot helper
// tot is the total conflict number
auto update_tot = [&tot](int cnt[]) {
    for (int i=0; i<10; ++i) {
        if (cnt[i] > 1) tot += cnt[i];
    }
};

// check row
for (int i=0; i<9; ++i) {
    int cnt[10] = {0};
    for (int j=0; j<9; ++j) {
        ++cnt[p->value(i, j)];
    }
    update_tot(cnt);
}

// check column
for (int i=0; i<9; ++i) {
    int cnt[10] = {0};
    for (int j=0; j<9; ++j) {
        ++cnt[p->value(j, i)];
    }
    update_tot(cnt);
}

// check block
for (int k=0; k<9; ++k) {
    int x = (k / 3) * 3;
    int y = (k % 3) * 3;
    int cnt[10] = {0};
    for (int i=x; i<x+3; ++i) {
        for (int j=y; j<y+3; ++j) {
            ++cnt[p->value(i, j)];
        }
    }
    update_tot(cnt);
}

return tot;
}

Can someone explain what this program is doing line by line? if possible. I'd appreciate it. Thank you so much!

I'm especially confused about this line:
auto update_tot = [&tot](int cnt[]) {