hdu hdu 1102 Constructing Roads(最小生成树Kruskal)

因为习惯用C++的sort函数在写cmp这个函数谓词时写成了

      int cmp(const void * a, const void * b) {
           edge * pa = (edge *)a;
           edge * pb = (edge *)b;
           return pa->w > pb->w;
      }

结果一直WA，最后发现这个函数只会返回1和0，从而导致排序出错。结果悲剧的一直WA。

以下是AC代码：

/*Author: ACb0yDate: 2010年9月15日23:23:50Type: MSTProblemId: hdu 1102 Constructing RoadsResult: AC*/#include <iostream>using namespace std;struct edge {int x, y;int w;};int n, q;int g[110][110];int father[110];edge edges[50100];int order[110];int find_set(int x) {if (x != father[x]) {return find_set(father[x]);}return x;}int cmp(const void * a, const void * b) {edge * pa = (edge *)a;edge * pb = (edge *)b;return pa->w - pb->w;}int main() {int i, j;#ifndef ONLINE_JUDGEfreopen("1102.txt", "r", stdin);#endifwhile (cin >> n) {for (i = 1; i <= n; i++) {for (j = 1; j <= n; j++) {cin >> g[i][j];}}cin >> q;for (i = 1; i <= q; i++) {int a, b;cin >> a >> b;g[a][b] = g[b][a] = 0;}int c = 0;for (i = 1; i <= n; i++) {for (j = i + 1; j <= n; j++) {edges[c].w = g[i][j];edges[c].x = i;edges[c].y = j;c++;}}qsort(edges, c, sizeof(edge), cmp);for (i = 1; i <= n; i++) {father[i] = i;order[i] = 0;}int ans = 0;for (i = 0; i < c; i++) {int x = find_set(edges[i].x);int y = find_set(edges[i].y);if (x != y) {ans += edges[i].w;father[x] = y;}}cout << ans << endl;}return 0;}