打印1-N

利用递归的先天条件排列组合

#include "stdafx.h"
#include <iostream> 
using namespace std;

void printBigInt(const char* c) {
    int i = 0;
    while (c[i] == '0') {
        ++i;
    }

    // not print zero
    if (i == strlen(c)) {
        return;
    }
    printf("%s\n", c + i);
}
void reSolver(char* c, int index, int len) {
    if (len == index) {
        printBigInt(c);
        return;
    }
    for (int i = 0; i < 10; ++i) {
        c[index] = i + '0';
        reSolver(c, index + 1, len);
    }
    return;
}

int main() {
    int n = 0;
    cin >> n;
    if(n <= 0) return;
    char* c = new char[n + 1];

    c[n] = '\0';
    reSolver(c, 0, n);

}

n 层 for 循环

#include <iostream> 
#include <vector>
#include <string>

using namespace std;

void printBigInt(const vector<char>& c) {
    int i = 0;
    while (c[i] == '0') {
        ++i;
    }

    // not print zero
    if (i == c.size()) {
        return;
    }

    cout << string(c.begin() + i, c.end()) << endl;
}

int main() {
    int n = 0;
    cin >> n;
    if (n <= 0) return 0;

    vector<char> c(n + 1, '0');
    c[n] = '\0';

    while (k >= 0) {
        printBigInt(c);
        int k = n - 1;
        while (k >= 0) {
            ++c[k];
            if (c[k] <= '9') {
                break;
            }
            else {
                c[k] = '0';
                --k;
            }
        }
    }

}