poj 3494 Largest Submatrix of All 1’s

       最近在学习单调桟，这个题目听有意思的，需要稍微动动心思，往poj 2559上想。但是时间总是1700MS左右，真不知道网上那些100ms是怎么出来的。

/** *  poj_3494.cpp * */#include <iostream>#include <cstdio>#include <cstring>using namespace std;#defineMN2010#define hpmax(a,b)((a)>(b)?(a):(b))#define hpmin(a,b)((a)<(b)?(a):(b))charmatrix[MN][MN];intbound[MN][MN], lmin[MN], rmin[MN];int stack[MN];int m, n, p;int main() {int i, j, ans, tmp, left, right;while ( scanf(" %d%d", &m, &n ) != EOF ) {for ( i = 1; i <= m; ++ i ) {for ( j = 1; j <= n; ++ j )scanf(" %c", &matrix[i][j] );}for ( i = 1; i <= m; ++ i ) {tmp = 0;for ( j = n; j >= 1; -- j ) {if ( '1' == matrix[i][j] ) ++ tmp;else tmp = 0;bound[i][j] = tmp;}} ans = 0;for ( j = 1; j <= n; ++ j ) {stack[0] = 0;bound[0][j] = -1;stack[1] = 1;lmin[1] = 0;p = 1;for ( i = 2; i <= m; ++ i ) {while ( p > 0 && bound[ stack[p] ][j] > bound[i][j] ) {rmin[ stack[p--] ] = i;}if ( bound[stack[p]][j] == bound[i][j])lmin[i] = lmin[ stack[p] ];else lmin[i] = stack[p];stack[++p] = i;}while ( p > 0 ) {rmin[ stack[p--] ] = m+1;}for ( i = 1; i <= m; ++ i ) {tmp = bound[i][j] * ( rmin[i] - lmin[i] - 1 );if ( tmp > ans )ans = tmp;}}printf("%d\n", ans );}return 0;}